fix(query-performance): Speed up permissioning in API

[macobo]

Problem

Dashboards load for a long time. Other endpoints suffer from similar overhead.

• Loading a dashboard with 10 insights was doing upwards of 90 queries total for calculating insight permissions
• Moving business logic out of models has both performance and maintainability benefits

Changes

• Consolidate user permissioning logic into a single file instead of spreading it across multiple
  • Adding a test suite for correctness
  • Adding performance shortcuts - avoiding repeated lookups, etc
• Update all callsites to use new pattern
• Remove effective_membership_level from team basic serializer as it was not needed and resulted in excessive load

How did you test this code?

• API tests
• Note I did not spend too much time adding new N+1 tests beyond ones in user_permissions.py - the main one was 90 queries with the old code.