DSL2: Add bedtools coverage

[jfy133]

for 1 to 1 parity with eager2

[shyama-mama]

@jfy133 I've added the bedtools coverage step from eager 2. I came up with a very ugly solution to get samtools view -H ${bam} | grep '@SQ' | sed 's#@SQ\tSN:\\|LN:##g' > genome.txt working using the existing samtools view module. But it seems to work. Let me know if there is a more graceful way to do this.

[jfy133]

Do you have a PR/branch I can look at the code at? If it's too hacky we can always make a local module :)

[jfy133]

*A local module meaning an unofficial module used only for this pipeline

[shyama-mama]

Pull request created here https://github.com/nf-core/eager/pull/1005