Add subworkflow commands create-test-yml, create and install

[mirpedrol]

Add commands create-test-yml, create and install (without installation of subworkflows modules) to the dev version of tools.

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

[drpatelh]

Thank you! 🚀

[codecov]

Codecov Report

Merging #1897 (da4d35e) into dev (60346c1) will decrease coverage by 4.08%.
The diff coverage is 20.51%.

❗ Current head da4d35e differs from pull request most recent head 54ca7f1. Consider uploading reports for the commit 54ca7f1 to get more accurate results

@@            Coverage Diff             @@
##              dev    #1897      +/-   ##
==========================================
- Coverage   64.39%   60.30%   -4.09%     
==========================================
  Files          35       37       +2     
  Lines        4179     4608     +429     
==========================================
+ Hits         2691     2779      +88     
- Misses       1488     1829     +341     

Impacted Files	Coverage Δ
nf_core/subworkflows/install.py	14.28% <14.28%> (ø)
nf_core/subworkflows/test_yml_builder.py	15.18% <15.18%> (ø)
nf_core/modules/modules_repo.py	73.45% <24.13%> (-7.86%)	⬇️
nf_core/__main__.py	53.30% <51.72%> (-0.21%)	⬇️

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