Extract meryl+merqury subworkflow into modules

[stephenturner]

PR #63 brings in changes that allow optionally passing in reads to support quality metrics that require them, such as using kmer counts from raw sequencing data to evaluate accuracy and completeness using Merqury (#42). @GallVp added a nice suggestion in #63 to extract a subworkflow into nf-core/modules that could be used across workflows.

See also:

• new subworkflow: merqury modules#6905 (new subworkflow issue in nf-core/modules -- after this is finished, come back to genomeqc here to use the subworkflow module

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Would be great to support the trio mode with parental reads. This is supported by the assemblyqc pipeline. Maybe, we can extract a sub workflow, put it on nf-core/modules so that the two pipelines can benefit from shared development. Please see the workflow on the assemblyqc repo:

https://github.com/Plant-Food-Research-Open/assemblyqc/blob/cec2728d0785d97e0e9493558c83d83d0b48240e/workflows/assemblyqc.nf#L598-L771

Originally posted by @GallVp in #63 (comment)

[stephenturner]

Note to self, useful docs:

• Docs: Create a subworkflow: https://nf-co.re/docs/nf-core-tools/subworkflows/create
• Docs: Writing nf-core modules and subworkflows: https://nf-co.re/docs/contributing/subworkflows