[IMP] common: add support for coverage minimum and precision t#58355

It's now possible to control the following parameters using environment variables:

• Minimum allowed coverage, using $COVERAGE_MIN
• Decimal precision, usin $COVERAGE_PRECISION

When the above variables are not set , values will fallback to their defaults, i.e. 0.

This was already implemented in the old CI [1] and added to the project template [2].

For more information, please check the configuration reference of Coverage.py on [3].

[1] https://github.com/Vauxoo/maintainer-quality-tools/pull/314
[2] https://git.vauxoo.com/vauxoo/project-template/commit/93bd8c1d
[3] https://coverage.readthedocs.io/en/coverage-5.0/config.html

Dummy MR:

• https://git.vauxoo.com/vauxoo/tanner-common/-/merge_requests/32