* 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"
Organization member's table is already scoped to an organization.
Rolename should avoid having the org_id appended.
Wipes all existing organization role assignments, which should not be used anyway.
Includes db schema and dbauthz layer for upserting custom roles. Unit test in `customroles_test.go` verify against escalating permissions through this feature.
