Release automation changes

[gsquared94]

This PR changes the github action trigger for release automation from PR with label 'draft-release' getting merged to commit with message 'release: vX.x.x' getting pushed. This solves 2 issues with current release automation:

• Release PRs created from forks didn't work since the github action triggered by forks didn't have permissions to create tags. Changing the trigger to be based on 'commits on master' will work even when release PRs are created from forks.
• Action triggered on PR merge was not repeatable manually in case of any error. Now we can simply push an empty commit if we want to retrigger the entire release pipeline again.

User facing changes:

Previously, in order to trigger the release pipeline, we required adding the draft-release label to the release PR and also Release vX.x.x be the PR title. Now we only require that the PR head commit be release: vX.x.x.

[codecov]

Codecov Report

Merging #5203 (5fdeb0d) into master (35214eb) will increase coverage by 0.05%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #5203      +/-   ##
==========================================
+ Coverage   71.82%   71.87%   +0.05%     
==========================================
  Files         387      387              
  Lines       13928    13928              
==========================================
+ Hits        10004    10011       +7     
+ Misses       3190     3187       -3     
+ Partials      734      730       -4     

Impacted Files	Coverage Δ
pkg/skaffold/docker/image.go	79.53% <0.00%> (+1.39%)	⬆️
pkg/skaffold/util/tar.go	56.00% <0.00%> (+5.33%)	⬆️

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[MarlonGamez]

This looks good imo, I think we can approve and merge once CI is fixed

[gsquared94]

Reran a few times to get a successful CI.