Provide projects readme.md with metric badges and setting merge request thresholds

[StefanSchubert]

Is your feature request related to a problem? Please describe.
To attract more senior contributors to the project and to be transparent according vital software engineering metrics I would love to have some of the fancy metrics on our readme.md

Describe the solution you'd like
The solution should not include any 3rd party product with license costs.
My first stride through possible solutions lead me here: https://github.com/cicirello/jacoco-badge-generator
which seems to be a good approach to the issue.

Describe alternatives you've considered
I also stumbled over this one: https://itnext.io/github-actions-code-coverage-without-third-parties-f1299747064d
but this solution would require a cloud storage for the badges, so I would give jacoco a chance.

Additional context
The jacoco badge generator relays on the output provided by this one:
https://dzone.com/articles/reporting-code-coverage-using-maven-and-jacoco-plu#

It would be good, if the code coverage is not being peerformed with each maven build as this might slow down local turnaround times.