New `Test Tags` setting as alias for `Force Tags` in RF 5.1

[bhirsz]

From https://github.com/robotframework/robotframework/issues/4368

It's part of the bigger refactor where Default Tags and Force Tags will be eventually removed - but in RF 6.0 and RF 7.0.

Rules needs to work with new alias Test Tags. We can also add deprecation warning for Force Tags.