[ci] use workflow rules

See merge request tools/frackit!196

Feature/improve coverage

See merge request tools/frackit!195

Feature/produce coverage page

See merge request tools/frackit!194

[ci] always include coverage in pipeline

See merge request tools/frackit!193

[cmake][coverage] do not use pretty-xml

See merge request tools/frackit!192

[ci] require manual start of pipeline in mrs

See merge request tools/frackit!191

Most of the time, changes to the docu will occur in header files, thus,
it should be checked not only if the doxygen setup in doc/ has changed.

This avoids the triggering of many pipelines during a phase of
development with an open merge request. For commits to master and for
tag commits, pipelines are still automatically started.

Fix/ci code coverage

See merge request tools/frackit!190

Feature/coverage reports

See merge request tools/frackit!188