add --coverage-package to cli

[FritzMatthaeus]

Use case

i have an app structured as a monorepo (without Melos, just a dart monorepo as all packages are only local):

structure:

• packages/foo
• lib/myapp

Running patrol test --coverage only covers the app files (which are in /lib) but not the files in the packages which contain the major part of the UI. This might be a case of a badly structured monorepo but it is what it is. It would be great if foo would be covered too.

I have found that flutter test does support including packages into the coverage by running:
flutter test --coverage --coverage-package foo

currently this is not supported by the Patrol CLI. For my purpose this would be a valuable feature

Proposal

include --coverage-package [mypackage] to Patrol CLI like
patrol test --coverage --coverage-package foo

[pdenert]

@gogolon could you please take a look?