Lint the modules.json for uninstalled modules

[KevinMenden]

This PR adds a new pipeline lint check (nf-core lint) which looks for module entries in the modules.json of modules that are not actually installed in the pipeline.

I thought it makes sense to package that into the nf-core lint command as it looks at a general pipeline file (modules.json) and compares that against all installed modules. The nf-core modules lint command is more module-centric, meaning that it runs specific lint tests for every module separately. Therefore I think it is more logical to add this check here.

PR checklist

• This comment contains a description of changes (with reason)
• CHANGELOG.md is updated
• If you've fixed a bug or added code that should be tested, add tests!
• Documentation in docs is updated

[codecov]

Codecov Report

Merging #1149 (47b83ba) into dev (7b8ae3f) will increase coverage by 0.05%.
The diff coverage is 85.00%.

@@            Coverage Diff             @@
##              dev    #1149      +/-   ##
==========================================
+ Coverage   69.27%   69.33%   +0.05%     
==========================================
  Files          50       51       +1     
  Lines        5237     5257      +20     
==========================================
+ Hits         3628     3645      +17     
- Misses       1609     1612       +3     

Impacted Files	Coverage Δ
nf_core/lint/modules_json.py	84.21% <84.21%> (ø)
nf_core/lint/__init__.py	75.20% <100.00%> (+0.10%)	⬆️

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[ErikDanielsson]

Looks good! Just found a few minor things.