In preparation for adding the "member" permission level, which will also
be grouped by org ID, do a bit of a refactor to make room for it and the
existing "org" level to live in the same `map`
* chore: refactor user subject logic to be in 1 place
* test: implement test to assert deleted custom roles are omitted
* add unit test for deleted role
* chore: create type for unique role names
Using `string` was confusing when something should be combined with
org context, and when not to. Naming this new name, "RoleIdentifier"
Includes db schema and dbauthz layer for upserting custom roles. Unit test in `customroles_test.go` verify against escalating permissions through this feature.
ケイラ