feat: add new required slug property to coder_app, use in URLs (#4573)

coderd/database/migrations/000067_app_display_name.up.sql

@@ -0,0 +1,9 @@
+BEGIN;
+
+-- rename column "name" to "display_name" on "workspace_apps"
+ALTER TABLE "workspace_apps" RENAME COLUMN "name" TO "display_name";
+
+-- drop constraint "workspace_apps_agent_id_name_key" on "workspace_apps".
+ALTER TABLE ONLY workspace_apps DROP CONSTRAINT IF EXISTS workspace_apps_agent_id_name_key;
+
+COMMIT;