Slskit

- Removed Python 3.8 support.
- Currently supported Python versions: 3.9.2, 3.10, 3.11, 3.12.5
- Currently supported Salt versions: 3006, 3007

- Added `os.environ` [interpolation](https://docs.python.org/3/library/string.html#template-strings) for `slskit.yaml` config files, e.g. `${PWD}` can be used to reference files relative to working directory.
- Added Python 3.12 support.
- Added Salt 3007 support.
- Removed Salt 3005 support.

- Added `--salt-output` parameter.
- Added Salt 3006 support.
- Removed Salt 3004 support.

- Added Salt 3005 support.
- Added Python 3.10 support.
- Removed Salt 3001, 3002 and 3003 support.
- Removed Python 3.7 support.

- Added Salt 3004 support.

- Added Salt 3003 support.
- Removed `snapshot create` and `snapshot check` commands. You can reproduce these commands like so:
- `slskit highstate > highstate.snap`
- `slskit highstate | diff highstate.snap -`