#### 📖 Summary
Adds `--driver-opt` buildx arg as plugin parameter. This should make it possible to pass through proxy settings.
#### 📑 Test Plan
> 💡 Select your test plan for the code changes.
- [x] CI pipeline tests
- Custom test
- No test plan
##### Details / Justification
Manually tested on own instance behind corporate proxy:

Unfortunately the `--build-arg` passthru seems not working
#### 📚 Additional Notes
- fixes#82
- still to do:
- [x] update docs
- [x] add usage example
> 💡NOTE: This is my first contribution in this codebase. Feedback and help is probably needed 😸
Reviewed-on: https://codeberg.org/woodpecker-plugins/docker-buildx/pulls/93
Reviewed-by: Patrick Schratz <pat-s@noreply.codeberg.org>
Co-authored-by: OCram85 <marco.blessing@googlemail.com>
Co-committed-by: OCram85 <marco.blessing@googlemail.com>