new subworkflow: fastq_remove_adapters_and_merge

[vagkaratzas]

Is there an existing subworkflow for this?

• [x] I have searched for the existing subworkflow

Is there an open PR for this?

• [x] I have searched for existing PRs

Is there an open issue for this?

• [x] I have searched for existing issues

Are you going to work on this?

• [x] If I'm planning to work on this subworkflow, I added myself to the Assignees to facilitate tracking who is working on the subworkflow

[vagkaratzas]

Difficulty: medium