missed: rules without matching plugins

Show keys from [tool.flakehell.plugins] that has no matched installed plugins. Exitcode of this command is equal to the number of missed plugins. For example:

[tool.flakehell.plugins]
pycodestyle = ["+*"]
"flake8-*" = ["+*"]

If you have installed only pyflakes and pycodestyle, command flakehell missed will show flake8-*. If you have also installed flake8-commas, the command will have the empty output.