chore: add CI and release workflow

[joshka]

The CI workflow is just a minimal one

The release workflow uses release-plz. If you haven't used it before, it's fairly simple. When you push changes to the main branch, it automatically keeps a CHANGELOG in sync with the changes and cuts a PR with an update to the CHANGELOG and version. Merging that PR automatically triggers a release of the project to crates.io.

You can see this in action in joshka/tui-big-text#21 - it's very easy to set and forget.

To enable this release workflow can you please:

1. Enable "Allow GitHub Actions to create and approve pull requests" (last checkbox at https://github.com/azorng/material/settings/actions)
2. Create a crate publish token at https://crates.io/settings/tokens. The token should have publish-update scope (it only needs to select this crate if you have multiple crates)
3. Add a new Repository secret named CARGO_REGISTRY_TOKEN at https://github.com/azorng/material/settings/secrets/actions with the token value

[joshka]

(working on fixing the tests in another PR)