Update bam2fastq10x to handle multiplexed samples

[herpov]

Changes

Currently, the module expects converted files to be located in the working directory prefixed with a given label. However, converting multiplexed samples result in nested directory structure. The prefix argument is used to name the top level directory. In the next level are two directories, one for GEX and one for CMO reads.

Thus, the update is simply changing the output path to expect a nested directory and collect all .fastq.gz files.

PR checklist

Closes #6725

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[herpov]

@grst, here is the PR I have created for the bamtofastq10x module. Do you know who is most relevant to ask for review on this?

[grst]

@BlueBicycleBlog is listed as maintainer in the meta.yaml