Add task.ext.suffix for CSVTK_CONCAT

[LeonHafner]

This PR adds support for specifying a custom suffix, so pipeline maintainers can work with files beyond just .csv and .tsv.

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[mahesh-panchal]

In my opinion the file ending should only be an input:. I don't see the case where a user needs to change it, as it could lead to downstream instability.

[LeonHafner]

I’m fine with any solution that lets me use it for files other than CSV and TSV.

[SPPearce]

@LeonHafner , what exactly do you want to be able to do?

[LeonHafner]

Currently, you can edit arbitrary text files delimited by any character by specifying the separator in the in_type and out_type inputs. However, the output file will always have a .csv or .tsv extension. This isn’t catastrophic, but it’s still poor practice, especially when working with formats like GFF.

[mahesh-panchal]

Our apologies for the delay in reviewing this, but there's a proposal open to the core team that needs voting that directly affects whether or not this pattern should be used. nf-core/proposals#69

[SPPearce]

One option is to just use the suffix of the original file.

[mahesh-panchal]

One option is to just use the suffix of the original file.

Does one need to worry about compression? Can this module read compressed input?