feat: Added a post-release workflow

[Rishab87]

What this PR does / why we need it:
This PR adds a post release workflow, which helps in creating a PR for merging back to main & promoting images with kpromo. This needs to be run manually after pre release is created and images have been built on prow. (For making this workflow run automatically, one approach we can take is create a PR in test-infra repo which curls a github API when image build is completed after which this workflow is triggered triggered, open to suggestions and other possible approaches).

Test PR: Rishab87#16

How does this change affect the cardinality of KSM: (increases, decreases or does not change cardinality)
does not changes

Which issue(s) this PR fixes: (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged)
Related to #2756

[k8s-ci-robot]

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This pull-request has been approved by: Rishab87
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