chore: Move AlertmanagerEndpoints validation to pkg/prometheus/server

[mviswanathsai]

Description

This PR moves the logic for storing AM endpoints to the store and the subsequent validation to pkg/prometheus/server as per comments on #6467.

Type of change

What type of changes does your code introduce to the Prometheus operator? Put an x in the box that apply.

• CHANGE (fix or feature that would cause existing functionality to not work as expected)
• FEATURE (non-breaking change which adds functionality)
• BUGFIX (non-breaking change which fixes an issue)
• ENHANCEMENT (non-breaking change which improves existing functionality)
• [ x] NONE (if none of the other choices apply. Example, tooling, build system, CI, docs, etc.)

Verification

Please check the Prometheus-Operator testing guidelines for recommendations about automated tests.

Changelog entry

Please put a one-line changelog entry below. This will be copied to the changelog file during the release process.

[mviswanathsai]

I don't understand why the generate and format action is failing.

[yp969803]

By looking at the error, the error is

lookup proxy.golang.org: no such host

The CI pipeline not able to resolve the DNS,

[mviswanathsai]

Right, I don't know if that has anything to do with the changes though.

[mviswanathsai]

@simonpasquier could you look into this?

[slashpai]

Looks to be sporadic issue, I have re-run the failed job lets see

[ArthurSens]

I believe we still have merge conflicts to solve here 😬