Pype 3: Define representation as data class

[create-issue-branch[bot]]

closes #1355

[BigRoy]

@antirotor

I'd like this get this to work with #2898 to hopefully streamline a lot of the Integration logic. However, publishing a subset, version and its representations tends to involve a lot more information than just the representation data.

My knowledge of attr (attrs?) library is relatively small and it'd be nice to bounce back and forth some discussions with regards to the overall implementation. Especially because there's a mismatch/difference between the instance.data["representations"] that OpenPype currently uses during publishing and what is actually written to the database in the end. They are not one to one the same data.

I was wondering if there's been more thought on this on OpenPype side regarding the "good" implementation of this and whether it'd be worth having a call about it before I try and give it a shot.

[antirotor]

Closing this as this needs fresh start with v4 in mind.