[alertmanager] Variable to add extra Pod Configurations

[rakesh-von]

What this PR does / why we need it

This PR lets users add additional Pod configs such as dnsPolicy and hostNetwork

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

Checklist

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

[rakesh-von]

@monotek - can you please review this change? We need this on an urgent basis. Sorry for this urgency.

[rakesh-von]

Hi @naseemkullah - can you please review this PR?

[rakesh-von]

HI @dongjiang1989 - thanks for reviewing, is it possible for you to merge this please?

[rakesh-von]

@monotek and @naseemkullah - can you please review this please? we are waiting for this change.