Add a way to determine the package version from git w/ new commits and dirty state

Perhaps adding a [git jinja function](https://rattler-build.prefix.dev/latest/experimental_features/#git-functions) that returns something akin to `git describe --tags --dirty`.

```
$ git describe --tags --dirty
v3.15.0a2-242-g453e9eebd5e-dirty
```

I would like to have the latest git tag, the current commit if `HEAD` is not the same as the tag, and the dirty state.