test: reset manager and team

[rflechtner]

re/ KILTProtocol/ticket#3671

Adds unit tests for changing/resetting pool manager and asset (admin) team.
To be rebased and merged after #785

Tests currently failing (fix TBD in another PR):

• Team cannot be reset when pool is not live (fixed by feat: reset team on refund #786)

Checklist:

• I have verified that the code works
  • No panics! (checked arithmetic ops, no indexing array[3] use get(3), ...)
• I have verified that the code is easy to understand
  • If not, I have left a well-balanced amount of inline comments
• I have left the code in a better state
• I have documented the changes (where applicable)
  • Either PR or Ticket to update the Docs
  • Link the PR/Ticket here