sambamba: add nf files

src/nf_modules/sambamba/index_bams.config

src/nf_modules/sambamba/index_bams.nf

src/nf_modules/sambamba/sort_bams.config

src/nf_modules/sambamba/sort_bams.nf

src/nf_modules/sambamba/split_bams.config

src/nf_modules/sambamba/split_bams.nf

src/nf_modules/sambamba/tests.sh