Support appending rules from installed packages

[zroger]

I would like to create a python package of my organization's custom rules, which could be installed alongside cfn-lint and then referenced from the CLI and/or .cfnlintrc by import path rather than directory path.

For example, with a custom package named myrules and a module within that package named recommended:

# install via pip
pip install cfn-lint
pip install myrules

# invoke via CLI
cfn-lint -a myrules.recommended ...

# or in .cfnlintrc
append_rules:
  - myrules.recommended

I'm happy to put together a PR if this is something that would be considered.

[kddejong]

I like this idea. I wonder how hard it would be to accomplish. I'm open to it.

[kddejong]

I believe this is complete. Closing. We can reopen if needed.