Adds support for Prometheus ServiceMonitor & adds missing Prometheus scraping annotations

[Shaked]

This PR adds support for Prometheus ServiceMonitor as part of #339 and fixes the missing Prometheus scraping annotations of #354 .

While the metricServer configuration is deprecated, I assume that it might be in use in some places and easier to set before migrating for some folks, so I have added the same support to it until it will be completely removed.

Checklist

• I have verified that my change is according to the deprecations & breaking changes policy
• Commits are signed with Developer Certificate of Origin (DCO - learn more)
• README is updated with new configuration values (if applicable)

Fixes #339
Fixes #354

[tomkerkhove]

LGTM, thank you!

[nguyenhoaibao]

@tomkerkhove when will this fix be released? I see the current latest version (v2.9.3) doesn't contain this fix.

[tomkerkhove]

This should be be shipped with KEDA v2.10 if I'm not mistaken as this is not impacting end-users; unless I'm mistaken ?

[fdebuire]

@tomkerkhove I am also waiting for the fix, according to #386 it has been released but the release seems not available:

helm search repo kedacore
NAME                                          	CHART VERSION	APP VERSION	DESCRIPTION
kedacore/keda                                 	2.9.3        	2.9.2      	Event-based autoscaler for workloads on Kubernetes

[JorTurFer]

You can see what is released on each version in the specific release branch, in this case for v2.9 https://github.com/kedacore/charts/tree/release/v2.9
As you can see, this PR isn't in the release branch, you can't trust in GH here because the commit "is released" as part of other chart

[fdebuire]

Sorry it's my bad, after doing a helm repo update I can see the 2.9.4version of the Helm chart

[JorTurFer]

Sorry it's my bad, after doing a helm repo update I can see the 2.9.4version of the Helm chart

no worries :)