Update allowed docs versions and add backfill workflow

[ndgrigorian]

This PR updates the allowed versions of dpctl docs in the dropdown, and adds a workflow to backfill old documentation versions.

This workflow is designed to allow passing a tag to the workflow and manually executing, creating and populating the folder for the tag

• Have you provided a meaningful PR description?
• Have you added a test, reproducer or referred to an issue with a reproducer?
• Have you tested your changes locally for CPU and GPU devices?
• Have you made sure that new changes do not introduce compiler warnings?
• Have you checked performance impact of proposed changes?
• Have you added documentation for your changes, if necessary?
• Have you added your changes to the changelog?
• If this PR is a work in progress, are you opening the PR as a draft?

[github-actions]

View rendered docs @ https://intelpython.github.io/dpctl/pulls/2312/index.html

[coveralls]

coverage: 75.476%. remained the same — update-allowed-docs-versions-and-add-backfill into master