Add subworkflow mapping statistics

[sainsachiko]

Add subworkflow MAPPING_STATISTICS #129 with:

• seqtk comp
• seqtk parse

Note: This subworkflow processes the output FASTA file from vcf2pseudogenome.py. However, this module has not yet been integrated into the main workflow. Therefore, mapping_statistics has been tested using independent data with a separate input channel.

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
  • If necessary, also make a PR on the nf-core/bactmap branch on the nf-core/test-datasets repository.
• Make sure your code lints (nf-core lint .).
• Ensure the test suite passes (nextflow run . -profile test,docker).
• 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).