Add quick detail on meta labels. (#4400)

* Add quick detail on meta labels.

* Add more technical details

* Fix extra *

* Update docs/sources/flow/reference/components/prometheus.scrape.md

Co-authored-by: Clayton Cornell <[email protected]>

* Update docs/sources/flow/reference/components/prometheus.scrape.md

Co-authored-by: Paschalis Tsilias <[email protected]>

---------

Co-authored-by: Clayton Cornell <[email protected]>
Co-authored-by: Paschalis Tsilias <[email protected]>

Author: 3 people

docs/sources/flow/reference/components/loki.write.md

@@ -204,6 +204,8 @@ loki.write "default" {
 }
 ```
 
-## Compression
+## Technical details
 
 `loki.write` uses [snappy](https://en.wikipedia.org/wiki/Snappy_(compression)) for compression.
+
+Any labels that start with `__` will be removed before sending to the endpoint. 

docs/sources/flow/reference/components/otelcol.receiver.jaeger.md

@@ -263,6 +263,6 @@ otelcol.exporter.otlp "default" {
 }
 ```
 
-## Compression
+## Technical details
 
 `otelcol.receiver.jaeger` supports [gzip](https://en.wikipedia.org/wiki/Gzip) for compression.

docs/sources/flow/reference/components/otelcol.receiver.otlp.md

@@ -219,6 +219,6 @@ otelcol.exporter.otlp "default" {
 }
 ```
 
-## Compression
+## Technical details
 
 `otelcol.receiver.otlp` supports [gzip](https://en.wikipedia.org/wiki/Gzip) for compression.

docs/sources/flow/reference/components/prometheus.receive_http.md

@@ -120,6 +120,6 @@ prometheus.remote_write "local" {
 }
 ```
 
-## Compression
+## Technical details
 
 `prometheus.receive_http` uses [snappy](https://en.wikipedia.org/wiki/Snappy_(compression)) for compression.

docs/sources/flow/reference/components/prometheus.remote_write.md

@@ -352,6 +352,9 @@ prometheus.remote_write "default" {
 }
 ```
 
-## Compression
+
+## Technical details
 
 `prometheus.remote_write` uses [snappy](https://en.wikipedia.org/wiki/Snappy_(compression)) for compression.
+
+Any labels that start with `__` will be removed before sending to the endpoint. 

docs/sources/flow/reference/components/prometheus.scrape.md

@@ -257,6 +257,19 @@ http://blackbox-exporter:9115/probe?target=grafana.com&module=http_2xx
 http://blackbox-exporter:9116/probe?target=grafana.com&module=http_2xx
 ```
 
-## Compression
+### Technical details
 
 `prometheus.scrape` supports [gzip](https://en.wikipedia.org/wiki/Gzip) compression.
+
+The following special labels can change the behavior of prometheus.scrape:
+* `__address__` is the name of the label that holds the `<host>:<port>` address of a scrape target.
+* `__metrics_path__`   is the name of the label that holds the path on which to scrape a target.
+* `__scheme__` is the name of the label that holds the scheme (http,https) on which to  scrape a target.
+* `__scrape_interval__` is the name of the label that holds the scrape interval used to scrape a target.
+* `__scrape_timeout__` is the name of the label that holds the scrape timeout used to scrape a target.
+* `__param__` is a prefix for labels that provide URL parameters used to scrape a target.
+
+Special labels added after a scrape
+* `__name__` is the label name indicating the metric name of a timeseries.
+* `job` is the label name indicating the job from which a timeseries was scraped.
+* `instance` is the label name used for the instance label.