Add Workflows to update version and create version tags

[egibs]

Closes: https://github.com/chainguard-dev/bincapz/issues/251

This PR adds two Workflows:

• One will create version update PRs via a workflow_dispatch (i.e., manually for now)
• One will create tags when commits are pushed to main (only if they do not exist)

In practice, the version update PRs will be merged with an updated version string which will then cause the tag Workflow to create a new tag matching that version.

Every other commit to main will result in the tag Workflow exiting without pushing any new tags since the current version's tag will already exist.

[egibs]

I plan on testing the PR creation at least. If that looks good, we can do real patch PR -> merge -> tag test.