Adding AlertManager SNS Receiver Implementation

[alanprot]

What this PR does:

• Updating Prometheus AlertManager dependency
  • Add AWS SNS receiver prometheus/alertmanager#2615
  • Ensure time interval comparisons are in UTC prometheus/alertmanager#2648
• Adding Support to SNS Receiver on AlertManager

Which issue(s) this PR fixes:

Checklist

• [NA] Tests updated
• Documentation added
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX]

[treid314]

Thanks! LGTM, Can you changelog entry to be with the other features to stick to format?

[alanprot]

Done and rebased! :D

[jeromeinsf]

Can you please also review this PR @alolita @Aneurysm9?

[bboreham]

Thanks! Couple of asks before merge:

Please fix the conflict (formatting in CHANGELOG), and also call out the update to Prometheus alertmanager code in the PR description.

Check what else gets picked up by the update - e.g. were there any major bug-fixes or deprecations in alertmanager between the old and new commits.

[alanprot]

Thanks @bboreham
I just rebased the branch and added the change set in the PR. We are bringing just 2 PRs.

[bboreham]

Thanks!

[treid314]

Thanks for adding the changes in Alertmanager to the PR!

[pracucci]

LGTM, thanks!