Add next calculated tag version to auto version via flag

It would be nice to get the next determined tag version from `auto version` by using a flag/argument instead of it only returning the applied label (patch, minor, major). In GitHub Actions, I currently combine `auto version` and `craig-day/compute-tag@v10` passing in the result of `auto version` to the `version_type` parameter of `craig-day/compute-tag@v10`

```
auto version --next-tag
...
Next version: v0.0.2
```

Current hack:
```
- id: auto_version
name: Get version bump type
env:
GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
run: |
VERSION_TYPE=$(~/.local/bin/auto version) && echo "VERSION_TYPE=${VERSION_TYPE}" >> "${GITHUB_ENV}"

- id: compute_tag
name: Compute next tag
uses: craig-day/compute-tag@v10
with:
github_token: ${{ github.token }}
version_type: ${{ env.VERSION_TYPE }}
```