Add GH actions for tags & releases

[moyerr]

Description

This PR introduces 3 GitHub Actions workflows:

1. create-tag.yml - A reusable workflow that can be invoked directly via dispatch (uncommon, usually for testing in isolation), or called by another workflow (common). This creates a tag on a specific git ref.
2. create-release.yml - A reusable workflow that can be invoked directly via dispatch (uncommon, usually for testing in isolation), or called by another workflow (common). This creates a release based on a given tag.
3. generate-tag-release.yml - A workflow that can be manually invoked to generate a version number, create a tag with the version number, and publish a release. In the future, this could be triggered via workflow call during deployments.

This PR also introduces 2 shell scripts to help with versioning:

1. gen-ver.sh - Generates a calendar version number (e.g. v25.05.21) based on the current date and any existing tags
2. inc-patch-ver.sh - Called within gen-ver.sh to either increment or add a patch version (in case there are multiple releases on the same calendar day).

Calendar Versioning

The versioning scheme introduced here uses zero-padded two-digit calendar versioning. For example, the first release on August 9, 2025 would be version v25.08.09.

To disambiguate multiple releases on the same calendar day, we add a patch version to the end. Versions without the patch component have an implicit .0 patch version. For example, the second release on August 9, 2025 would be version v25.08.09.1.