docs: Fix prometheus port regex

[JBodkin-Amphora]

The example documentation in prometheus has a different regex pattern compared cilium. In some instances, prometheus or the opentelemetry collector is not picking up the correct port, because the relabel config is not applying since the regex doesn't match.

[maintainer-s-little-helper]

Commit 8e7a979 does not match "(?m)^Signed-off-by:".

Please follow instructions provided in https://docs.cilium.io/en/stable/contributing/development/contributing_guide/#developer-s-certificate-of-origin

[lambdanis]

/test

[lambdanis]

Thank you @JBodkin-Amphora.

It looks like the original examples come from some ancient version of Prometheus like v0.19.0. On a side note, Cilium docs around Prometheus could use a general refresh IMO, hopefully one day :)