feat(external-registry): Implement CRUD operations and connection verification for external registries

ts/classes.cloudly.ts

@@ -137,6 +137,7 @@ export class Cloudly {
 
     // start the managers
     this.imageManager.start();
+    this.externalRegistryManager.start();
   }
 
   /**
@@ -149,5 +150,6 @@ export class Cloudly {
     await this.secretManager.stop();
     await this.serviceManager.stop();
     await this.deploymentManager.stop();
+    await this.externalRegistryManager.stop();
   }
 }