[TUF] Succinct hashed bin delegations

[nate-double-u]

Improve hashed bin delegations in TUF by adding succinct hashed bin delegations to the python-tuf reference implementation. TUF delegations allow the repository to specify which developer (or signing key) is associated with which packages are downloaded using TUF. Hashed bin delegations allow TUF to delegate many projects to the same signing keys more efficiently. However, the current implementation has a lot of duplicated metadata that can be simplified without affecting the functionality of this feature. This project would be implementing these simplifications to hashed bin delegations.

Mentors: Marina Moore (@mnm678), Lukas Pühringer (@lukpueh), Zack Newman (@znewman01)

https://github.com/cncf/mentoring/blob/main/summerofcode/2022.md#succinct-hashed-bin-delegations