Ability to set a default team for new members to be added to

### Problem Statement See https://github.com/getsentry/sentry/issues/44013 for first request Use case - users that are added to the organization but not to any teams cannot be "Assigned To" on issues. Having a default team fixes this issue. Alternatively, if you could just make it so that teamless members can be assigned to for issues, that would also suit my purposes :) ### Solution Brainstorm _No response_ ### Product Area Settings - Teams