[prometheus] Use Alertmanager API port only for kubernetes_sd.

[anas-aso]

Signed-off-by: Anas anas.oubrahim@commercetools.com

What this PR does / why we need it:

Avoid sending alerts to Alertmanager Peering port.

Which issue this PR fixes

(optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged)

• fixes #

Special notes for your reviewer:

In this PR : #179 the mesh peering port was explicitly defined for Alertmanager pods, as a result kubernetes_sd will list it as a target for Prometheus to send alerts to.
This leads to the following error on Prometheus spamming the logs:

{"alertmanager":"http://10.35.102.55:6783/api/v1/alerts","caller":"notifier.go:527","component":"notifier","count":2,"err":"Post \"http://10.35.102.55:6783/api/v1/alerts\": EOF","level":"error","msg":"Error sending alert","ts":"2020-11-12T16:45:09.526Z"}

Checklist

• DCO signed
• Chart Version bumped
• Title of the PR starts with chart name (e.g. [prometheus-couchdb-exporter])