SAMtools: add nf and test scripts

src/nf_modules/SAMtools/samtools.config

src/nf_modules/SAMtools/samtools.nf

src/nf_modules/SAMtools/tests/filter_bams.nf

src/nf_modules/SAMtools/tests/index_bams.nf

src/nf_modules/SAMtools/tests/sort_bams.nf

src/nf_modules/SAMtools/tests/split_bams.nf

src/nf_modules/SAMtools/tests/tests.sh