Update modules lint to check git commit of modules

[KevinMenden]

Use the modules.json file to check whether the git commits (i.e. versions) of modules are the most recent ones and warn if not.

[KevinMenden]

Features to implement:

• check if modules.json exists (--> files_exist of nf-core lint)
• check that all nf-core modules have an entry in modules.json
• warn if new commit versions are available
• verify that the file content fits the commit message --> this can be done by the modules_changes lint test just by using the git_sha