Host removal parameter - pre-built bowtie2 index

[simone-pignotti]

Description of feature

Hi,

In the host removal module, the bowtie index needs to be recomputed from --host_fasta for each execution. Would it be possible to add --host_bt2 or similar to point to a pre-built index prefix? The logic is already implemented for the --host_genome option, where pre-built indexes from iGenomes are used.

Thanks Simone