Add ability to get version from git tags

if `setup` is called with `use_vcs_version=True`, then the version is obtained by doing `git describe --tags --dirty`.

e.g.:

```
# setup.py

from setuptools import setup

setup(name='profilesvc',
      use_vcs_version=True)
```

```
$ python setup.py egg_info; grep '^Version:' profilesvc.egg-info/PKG-INFO
...
Version: v23.0.2-develop-4-g79f3bc0-dirty
```

Cc: @sudarkoff