Add TCRdock tool for TCR:pMHC structure prediction

[eliasball]

Changes

This PR adds the TCRdock tool as a mode option to proteinfold. It is a specialized version of AlphaFold focused on TCR:pMHC prediction. The integration into the pipeline was created as part of my bachelors thesis.

Notes

• TCRdock uses a way different samplesheet, defining not sequences but rather allele variants and so on. Therefore I also added documentation about this different samplesheet.
• Some small changes still need to be made by me before the PR should be accepted. E.g. tests and the publishing of the required Docker container are still missing.

PR checklist

• This comment contains a description of changes (with reason).
• If you've fixed a bug or added code that should be tested, add tests!
• If you've added a new tool - have you followed the pipeline conventions in the contribution docs
• Make sure your code lints (nf-core lint).
• Ensure the test suite passes (nextflow run . -profile test,docker --outdir <OUTDIR>).
• Usage Documentation in docs/usage.md is updated.
• Output Documentation in docs/output.md is updated.
• CHANGELOG.md is updated.
• README.md is updated (including new tool citations and authors/contributors).