Release workflow

[HugoOnghai]

adds the release workflow for our mpcite package.

it uses uv, testpypi, charmixer's auto-changelog action, mkdocs...

uv

• uv publish is used to publish to testpypi. the keyword options will need to change when switching to pypi.
• uv version bumping (e.g. uv version --bump patch) is left up to the user to do, before a release is published (and it should fail to publish if the version wasn't bumped)

testpypi

• currently at https://test.pypi.org/project/mp-cite/
• the github action is provided a write-access testpypi api token in order to uv publish. the token is scoped to only work on the mpcite project on testpypi

auto-changelog

• follows the steps done by emmet's release workflow
• haven't yet tested if it works

mkdocs

• uvx mkdocs gh-deploy builds and deploys the project. no need for a deployment action to be called. pretty neat!
• the documentation is currently hosted at (https://hugoonghai.github.io/MPCite/)

Misc... to dos...

• As of making this PR, the workflow will also run when the release-workflow branch is pushed. this is need to be changed later
• idk how to actually make a release yet so I will figure this out soon too