Debug metrics not listed in the docs of many Promethus-based components

[ptodev]

Request

Take the "Debug metrics" section of the discovery.consul docs for example:

• It should list metrics such as prometheus_sd_consul_rpc_failures_total. Instead, it says there are no metrics.
• As per the Writing documentation for Flow components doc, the "Debug metrics" section should be a major section - ##, but instead it is a ### heading.

The same issues exist for other Prometheus-based components as well.

There is also a similar issue for Otel components - #384.

Use case

More accurate docs.

[github-actions]

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