Put change behind a FF

src/feature-flags.ts

@@ -77,6 +77,7 @@ export enum Feature {
   QaTelemetryEnabled = "qa_telemetry_enabled",
   /** Note that this currently only disables baseline file coverage information. */
   SkipFileCoverageOnPrs = "skip_file_coverage_on_prs",
+  StartProxyRemoveUnusedRegistries = "start_proxy_remove_unused_registries",
   StartProxyUseFeaturesRelease = "start_proxy_use_features_release",
   UploadOverlayDbToApi = "upload_overlay_db_to_api",
   UseRepositoryProperties = "use_repository_properties_v2",
@@ -328,6 +329,11 @@ export const featureConfig = {
     // cannot be found when interpreting results.
     minimumVersion: undefined,
   },
+  [Feature.StartProxyRemoveUnusedRegistries]: {
+    defaultValue: false,
+    envVar: "CODEQL_ACTION_START_PROXY_REMOVE_UNUSED_REGISTRIES",
+    minimumVersion: undefined,
+  },
   [Feature.StartProxyUseFeaturesRelease]: {
     defaultValue: false,
     envVar: "CODEQL_ACTION_START_PROXY_USE_FEATURES_RELEASE",