adopt merge-release-to-master workflow

[johncowen]

Description

Adopt: https://github.com/kumahq/kuma/blob/master/.github/workflows/merge-release-to-master.yaml

We discussed several options here, and as the above workflow immediately merges any merged PRs back to master we prefer this to:

1. Cherry picking (we lose the reference on master to where the commit came from
2. Waiting a long period of time and then merging all changes made back to master

i.e. we are essentially "fixing it where it broke and forward porting"

Related/some discussion #3710