reverse_tunnel: propagate initiator worker and connection ids

[roll-no-21]

Commit Message: reverse_tunnel: propagate initiator worker and connection ids

Additional Description:
The reverse-tunnel handshake carried no way to distinguish tunnels opened by different worker threads or connections of the same initiator. This adds two optional handshake headers and surfaces them on both ends so operators can tell tunnels apart and correlate a tunnel across the initiator and acceptor.

Downstream (initiator). RCConnectionWrapper::connect() now sends x-envoy-reverse-tunnel-worker-id (the initiator worker dispatcher name, e.g. worker_2) and x-envoy-reverse-tunnel-connection-id (the initiator's per-connection id). Both are exposed in the initiator access log via the new worker_id and connection_id fields of the envoy.reverse_tunnel.initiator dynamic metadata namespace. The connection id is captured at socket handoff so it is still available for the connection_closed event after the connection object is gone.

Upstream (acceptor). The envoy.filters.network.reverse_tunnel filter parses the two headers (best-effort; empty for older initiators) and threads them through addConnectionSocket into ReverseTunnelLifecycleInfo. They are emitted on every reverse-tunnel lifecycle event as the initiator_worker_id and initiator_connection_id fields of the envoy.reverse_tunnel.lifecycle dynamic metadata namespace, and as the envoy.reverse_tunnel.initiator_worker_id / envoy.reverse_tunnel.initiator_connection_id connection filter-state keys. These are distinct from the acceptor's own worker field.

Both directions are additive and backward compatible: an initiator that does not send the headers yields empty values, and no configuration changes are required.

Risk Level: Low
Testing: Unit tests added/updated across the downstream initiator, the acceptor socket manager, the lifecycle filter, and the network filter parse path. Full //test/extensions/bootstrap/reverse_tunnel/..., //test/extensions/filters/network/reverse_tunnel/..., and //test/extensions/clusters/reverse_connection/... suites pass.
Docs Changes: Updated docs/root/configuration/other_features/reverse_tunnel.rst (lifecycle metadata fields + filter-state keys, initiator access-log field table) and the initiator example config.
Release Notes: Added a new_features changelog entry.

This pull request and its description were written by Isaac.

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Caused by: #46232 was opened by roll-no-21.

see: more, trace.

[roll-no-21]

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