Motivation
It makes sense to separate the pytest config from coverage config since they can basically be in independent files:

1. We might mix pyproject.toml config for coverage with non-pyproject.toml for pytest (see All pytest configuration methods should be supported #185).
2. There are different config files than just pyproject.toml for coverage too and the logic will get too complicated in the one tool. (See Properly handle coverage configuration files #221)

It can have its own interface, usethis tool coverage. usethis tool pytest should not longer use coverage by default.

Summary of desired enhancement
Implement usethis tool coverage separate from usethis tool pytest