Add a Find/Concatenate module

[BioWilko]

This module is HEAVILY based on the CAT/CAT module, the difference being that it uses find to concatenate files iteratively therefore avoiding wildcard expansion, this allows any number of files to be concatenated since it doesn't run into the argument limit.

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 module conventions in the contribution docs
• If necessary, include test data in your PR.
• Remove all TODO statements.
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• Use BioConda and BioContainers if possible to fulfil software requirements.
• Ensure that the test works with either Docker / Singularity. Conda CI tests can be quite flaky:
  • For modules:
    • nf-core modules test <MODULE> --profile docker
    • nf-core modules test <MODULE> --profile singularity
    • nf-core modules test <MODULE> --profile conda
  • For subworkflows:
    • nf-core subworkflows test <SUBWORKFLOW> --profile docker
    • nf-core subworkflows test <SUBWORKFLOW> --profile singularity
    • nf-core subworkflows test <SUBWORKFLOW> --profile conda

[jfy133]

I've updated the meta for you, left one comment but I think it's OK assuming tests pass - I would like to get second pair of eyes though

[jfy133]

I think other than removing the maybe unnecessary commented out test assertions we are good to go?