chore: implement databased backend for custom roles (#13295)

Includes db schema and dbauthz layer for upserting custom roles. Unit test in `customroles_test.go` verify against escalating permissions through this feature.

coderd/database/migrations/000209_custom_roles.up.sql

@@ -0,0 +1,26 @@
+CREATE TABLE custom_roles (
+	-- name is globally unique. Org scoped roles have their orgid appended
+	-- like:  "name":"organization-admin:bbe8c156-c61e-4d36-b91e-697c6b1477e8"
+	name text primary key,
+	-- display_name is the actual name of the role displayed to the user.
+	display_name text NOT NULL,
+
+	-- Unfortunately these values are schemaless json documents.
+	-- If there was a permission table for these, that would involve
+	-- many necessary joins to accomplish this simple json.
+
+	-- site_permissions is '[]Permission'
+	site_permissions jsonb NOT NULL default '[]',
+	-- org_permissions is 'map[<org_id>][]Permission'
+	org_permissions jsonb NOT NULL default '{}',
+	-- user_permissions is '[]Permission'
+	user_permissions jsonb NOT NULL default '[]',
+
+	-- extra convenience meta data.
+	created_at timestamp with time zone NOT NULL DEFAULT CURRENT_TIMESTAMP,
+	updated_at timestamp with time zone NOT NULL DEFAULT CURRENT_TIMESTAMP
+);
+
+-- Ensure no case variants of the same roles
+CREATE UNIQUE INDEX idx_custom_roles_name_lower ON custom_roles USING btree (lower(name));
+COMMENT ON TABLE  custom_roles IS 'Custom roles allow dynamic roles expanded at runtime';