Squlearn

New Contributors
* MHagelueken made their first contribution in https://github.com/sQUlearn/squlearn/pull/185

**Full Changelog**: https://github.com/sQUlearn/squlearn/compare/v0.4.0...v0.5.0

- OPflow & QI mitigation
- rename `feature_map` to `encoding_circuit`
- rename `expectation_operator` to `observables`
- better tests
- test workflow
- clean QNN output
- user guide for QNNs
- improved documentation

- add a bunch of documentation
- add some tests:
- qnns
- qsvm
- qkrr
- add get_params and set_params for high level methods
- github action workflows:
- check if documentation can be built on PR
- publish documentation on release

- fix memory leak
- fix bug in feature stacking
- add github workflows
- formatting checks
- build and release
- change to flit build system + pyproject
- add some documentation

Early access version (0.1.0) of sQUlearn.