Add SonarCloud CI
Mentioned at https://github.com/adsharma/py2many/issues/191#issuecomment-866498863 , SonarQube provides quite good analysis for a lot of languages.  There is a cloud CI provider, sonarcloud.io, which only provides the default/official plugins, which sadly excludes Rust, but it is still useful.  It also provides a way to record coverage; while it isnt as mature of codecov.io, it is quite good.

As can be seen at https://sonarcloud.io/summary/new_code?id=jayvdb_py2many it would have detected the problem being fixed by https://github.com/adsharma/py2many/pull/344

The automatic analysis is enabled at Administration -> Analysis Method, ignore the fact it is not recommended. Then I suggest setting the "New Code" to Number of days : `10`

We can disable code smells for test cases under Administration -> General Settings -> Analysis Scope setting "Source File Exclusions"