[DynamicPlugin] Determine if the page is loaded

Code is in place to check if the page is loaded.  If loaded, then the backend APIs aren't called to retrieve data.  We need to revisit this in the context of the dynamic plugin.

In the initial GitOps dynamic plugin, I hacked it such that we simply check if the array is non-empty. 

Acceptance Criteria:

• Confirm that useK8sWatchResource hook is working well and namespaces data is correctly loaded in GitOpsListPage.tsx component in the dynamic plugin context.  eg. ensure that we are not constantly calling the backend APIs to getManifestURLs and fetchAllAppGroups

Update Aug 26, 2022: SDK has advanced more, as Yi found out in the comment below. At minimum, we need to test this and if verified we don't thrash the backend, then this story can be closed.