feat(Utils): add tool to convert reference PAS bed to gtf

[ninsch3000]

Some tools require a file of reference poly(A) sites. The format of this reference for some tools is bed, for others gtf.
The reference we are going to use will most likely come in bed format. Thus, we need a util to transform this reference to gtf.

Inspirations:
https://github.com/pfurio/bed2gtf
https://www.biostars.org/p/64346/