xDS Documentation: Updated proto reference

Took me a bit, but now I understand how more of the xDS implementation
works!

This should update the documentation appropriately now.

docs/src/services/xds.md

@@ -33,27 +33,15 @@ As described within the [xDS-api] documentation, the xDS API comprises a set of
 specific set of configuration resource types, while the protocol itself comes in several [variants][xds-variants].
 Quilkin implements the **Aggregated Discovery Service (ADS)** _[Incremental xDS][incremental-xds]_ variant with gRPC.
 
-## Supported APIs
+## xDS Configuration Resources
 
-Since the range of resources configurable by the xDS API extends that of Quilkin's domain (i.e being UDP based, Quilkin does not have a need for HTTP/TCP resources), only a subset of the API is supported. The following lists these relevant parts and any limitation to the provided support as a result:
+Heavily influenced by xDS's [Cluster Discovery Service][CDS], [Endpoint Discovery Service][EDS], and 
+[Listener Discovery Service][LDS], Quilkin utilises its own custom Configuration xDS resources 
+[(reference)][config.proto] to enable dynamic configuration of Datacenters, Clusters, Endpoints and Filters through 
+the Aggregated Discovery Service.
 
-- **Cluster Discovery Service [(CDS)][CDS]**: Provides information about known clusters and their membership information.
-  * The proxy uses these resources to discover clusters and their endpoints.
-  * While cluster topology information like [locality] can be provided in the configuration, the proxy currently does not use this information (support may be included in the future however).
-  * Any [load balancing information][lbpolicy] included in this resource is ignored. For load balancing, use [Quilkin filters][filters-doc] instead.
-  * Only [cluster discovery type] `STATIC` and `EDS` is supported. Configuration including other discovery types e.g `LOGICAL_DNS` is rejected.
-
-- **Endpoint Discovery Service [(EDS)][EDS]**: Provides information about endpoints.
-  * The proxy uses these resources to discover information about endpoints like their IP addresses.
-  * Endpoints may provide [Endpoint Metadata][endpoint-metadata] via the [metadata][xds-endpoint-metadata] field. These metadata will be visible to filters as part of the corresponding endpoints information when processing packets.
-  * Only [socket addresses] are supported on an endpoint's address configuration - i.e an IP address and port number combination. Configuration including any other type of addressing e.g named pipes will be rejected.
-  * Any [load balancing information][clapolicy] included in this resource is ignored. For load balancing, use [Quilkin filters][filters-doc] instead.
-
-- **Listener Discovery Service [(LDS)][LDS]**: Provides information about [Filters and Filter Chains][filters-doc].
-  * Only the `name` and `filter_chains` fields in the [Listener resource][listener-resource] are used by the proxy. The rest are ignored.
-  * Since Quilkin only uses one filter chain per proxy, at most one filter chain can be provided in the resource. Otherwise the configuration is rejected.
-  * Only the list of [filters][xds-filters] specified in the [filter chain][xds-filter-chain] is used by the proxy - i.e other fields like `filter_chain_match` are ignored. This list also specifies the order that the corresponding filter chain will be constructed.
-  * gRPC proto configuration for Quilkin's built-in filters [can be found here][filter-protos]. They are equivalent to the filter's static configuration.
+This [above reference][config.proto] also provides documentation for all the ProtoBuf definitions for all 
+[Filters][filters-doc] that are available in Quilkin.
 
 ## Connecting to an xDS management server
 
@@ -66,22 +54,13 @@ the `management_servers` [command line](../../api/quilkin/struct.Proxy.html#stru
 [envoy proxy]: https://www.envoyproxy.io/docs/envoy/latest/
 [xDS-protocol]: https://www.envoyproxy.io/docs/envoy/latest/api-docs/xds_protocol#the-xds-transport-protocol
 [xDS-api]: https://www.envoyproxy.io/docs/envoy/latest/intro/arch_overview/operations/dynamic_configuration
+[config.proto]: ./xds/proto/index.md#quilkin_config_v1alpha1_config-proto
 [CDS]: https://www.envoyproxy.io/docs/envoy/latest/intro/arch_overview/operations/dynamic_configuration#cds
 [EDS]: https://www.envoyproxy.io/docs/envoy/latest/intro/arch_overview/operations/dynamic_configuration#eds
 [LDS]: https://www.envoyproxy.io/docs/envoy/latest/intro/arch_overview/operations/dynamic_configuration#lds
-[cluster discovery type]: https://www.envoyproxy.io/docs/envoy/latest/api-v3/config/cluster/v3/cluster.proto#enum-config-cluster-v3-cluster-discoverytype
-[lbpolicy]: https://www.envoyproxy.io/docs/envoy/latest/api-v3/config/cluster/v3/cluster.proto#enum-config-cluster-v3-cluster-lbpolicy
-[clapolicy]: https://www.envoyproxy.io/docs/envoy/latest/api-v3/config/endpoint/v3/endpoint.proto#config-endpoint-v3-clusterloadassignment-policy
 [locality]: https://www.envoyproxy.io/docs/envoy/latest/api-v3/config/core/v3/base.proto#config-core-v3-locality
-[socket addresses]: https://www.envoyproxy.io/docs/envoy/latest/api-v3/config/core/v3/address.proto#config-core-v3-address
 [filters-doc]: ./proxy/filters.md
-[listener-resource]: https://www.envoyproxy.io/docs/envoy/latest/api-v3/config/listener/v3/listener.proto#config-listener-v3-listener
-[xds-filters]: https://www.envoyproxy.io/docs/envoy/latest/api-v3/config/listener/v3/listener_components.proto#envoy-v3-api-msg-config-listener-v3-filter
-[xds-filter-chain]: https://www.envoyproxy.io/docs/envoy/latest/api-v3/config/listener/v3/listener_components.proto#config-listener-v3-filterchain
 [xds-variants]: https://www.envoyproxy.io/docs/envoy/latest/api-docs/xds_protocol#variants-of-the-xds-transport-protocol
 [filter-protos]: https://github.com/googleforgames/quilkin/tree/{{GITHUB_REF_NAME}}/proto/quilkin/filters
 [xds-endpoint-metadata]: https://www.envoyproxy.io/docs/envoy/latest/api-v3/config/core/v3/base.proto#envoy-v3-api-msg-config-core-v3-metadata
-[endpoint-metadata]: proxy.md#endpoint-metadata
-[control-plane]: https://github.com/googleforgames/quilkin/tree/{{GITHUB_REF_NAME}}/xds
-[Kubernetes]: https://kubernetes.io/