Add minimap2 as aligner option for Bismark

Description of feature

As requested by @sateeshperi, it would be nice to support minimap2 as alternative aligner for Bismark. Here are the options that are currently supported:

MINIMAP2-SPECIFIC OPTIONS:

--minimap2/--mm2

Uses minimap2 as the underlying read aligner. This mode is very new and currently experimental. The default mapping mode is --nanopore (preset -x map-ont (Nanopore reads)). Currently, there are no plans to support PacBio reads. Internally, minimap2 is run with the options -a --MD. More information here: https://lh3.github.io/minimap2/minimap2.html. Default: OFF.

--mm2_nanopore

Using the minimap2 preset for Oxford Nanopore (ONT) vs reference mapping (-x map-ont). Only works in conjunction with --minimap2. Default mode when --minimap2 is specified without additional qualifiers.

--mm2_pacbio

Using the minimap2 preset for PacBio vs reference mapping (-x map-pb). Only works in conjuntion with --minimap2. Default: OFF.

--mm2_short_reads

This option invokes the minmap2 preset setting -x sr and is intended for genomic short-read mapping with accurate reads (probably Illumina 150bp+ ?). For spliced short-reads, please use --hisat2 instead. The sr preset mode (short single-end reads without splicing) uses the following options: -k21 -w11 --sr --frag=yes -A2 -B8 -O12,32 -E2,1 -r50 -p.5 -N20 -f1000,5000 -n2 -m20 -s40 -g200 -2K50m --heap-sort=yes --secondary=no. Default: OFF.

--mm2_maximum_length <int>

Maximum length cutoff for very long sequences (currently allowed 100-100,000 bp). Default: 10000.

Start by locating the existing Bismark aligner option in the methylseq workflow and compare its interface with the minimap2 options listed in the issue and linked minimap2 documentation. Done means the requested minimap2 modes and maximum-length cutoff are supported as Bismark alternatives, with the relevant workflow checks passing.