feat(Summary workflows): new SWF for relative usage quantification

#332 was dismissed, instead we'll have an additional SWF for relative quantification
- Check #373 for input file formats
- Check #301 and new issues for filtering of GT
- Check #413 for a discussion on how to define an identifier for terminal exons & PAS from ground truth & prediction
- Check #399 for proof-of-concept implementation of filtering, site matching & metric calculation
- Check #278 for an initial discussion on how to calculate relative expression, qualifying tools etc.
- Check #413 for a https://github.com/iRNA-COSI/APAeval/issues/413

### Create new issues
* [ ] relative usage metrics specifications
* [ ] relative usage metric calculations
* [ ] relative usage swf backbone
* [ ] relative usage swf testing

~~Implementations are still blocked by #374~~

Start by reading the linked discussions in #373, #301, #413, #399, and #278, then confirm whether #374 still blocks implementation. The work is split into specifications, relative-usage metric calculations, an SWF backbone, and testing; it is done when each of these has a defined implementation and validation path.

Written by the indexing model from the issue text.