Refactor for Project Role assignments for Team #807

[Raz Ben Simon]

The same as we did

1. here for Organization Level assignments (team only).
2. here for Environment Level assignments (team + user).

We want to achieve the same for the new Project level Team assignments API.

We already implemented this but we now have synced our project team level to the new API too.
meaning we deprecating the old APIs, so we need to adjust the old resources related to Project<-->Team role assignments.

deprecated APIs:

1. updateAssignments
2. deleteSingleAssignment
3. createOrUpdateSingleAssignment
4. getAssignments

new API:
Use the new Team Role APIs: Get, Upsert, Delete.
Same API as before, we just add projectId.

[Raz Ben Simon]

note that exisiting assignments still has the same id. so I hope we good regarding statefile plan changes

[Raz Ben Simon]

cc @sagydr @yarivg

[Tomer Heber]

Feature is released. I'm keeping it open because I still want to make additional refactoring.