#252: Updated Github workflows from Exasol toolbox

[tomuben]

fixes #252

1. Update GH workflows via tbx workflow update but
   a) Removed GH page generation
   b) Removed report metrics (still using legacy UnitTest FW. After switching to pytest we can reconsider creation of metrics)
2. Adjusted slow tests to run in parallel (like before)
3. Created a nox task for generation of list of integration tests and removed the bash script
4. Created new environment manual-approval and changed branch protect rules to require Allow Merge
5. Created new repository secrets DOCKER_USERNAME and DOCKER_PASSWORD. The environments ci_test and publish can be removed (the secrets were before part of the environments)

[tomuben]

Created by tbx workflow update