Add invitation backoffice tests

- Add base invitation view test case
- Add tests for both directions of habitat invitations
  - Habitat to assembly
  - Assembly to habitat
- Add decision tests
  - Accept
  - Withdraw
  - Reject including resending
  - Update
- Add permission tests
- Add invalid interaction tests
  - Add invalid action tests
  - Add invalid invitation type test
  - Add missing requester id test
  - Add duplicate invitation tests