st2_finalize_release action is not idempotent

[Kami]

Right now st2cd.st2_finalize_release workflow is not idempotent which means that if it fails halfway through it's a huge PITA to re-run it since not all tasks are idempotent.

We should fix mistral_tag_release, st2_tag_release and other tasks in the workflow to be idempotent - if tags already exist, we should simply proceed with a next task in the workflow.