Setup the Gitlab-CI/CD

The automation of some workflows regarding the development of minterpy shall be done using the GitLab-CI/CD. This was also suggested here #35 .

The CI/CD shall include:

• build minterpy
• deploy minterpy to PyPi and Conda forge
• run the unittests and deploy the test results (passing status and coverage)
• build the docs
• deploy the docs to GitLab-Pages (with the domain minterpy)

The Pipeline shall trigger on MRs to dev and merges to main and dev. The deployed artefacts shall be linked in the README.md (via the respective badge).