Dashboard should send repository cluster with assetsvc requests

[absoludity]

Description:

When requesting the catalog of charts available for a namespace on a cluster, the auth-gate ensures the requestor has access to that namespace and cluster (e.g. /api/assetsvc/v1/clusters/second-cluster/namespaces/default/charts ) and so is cluster-aware, but then forwards the request so the assetsvc which responds with all charts available for use in that namespace (non-cluster aware).

Similarly, when viewing a specific chart, a request to the assetsvc will use the repository namespace (which could be the current namespace or the global namespace) but always the current cluster (as there is no concept yet of a repository cluster in the dashboard).

We can fix both issues simply by updating the assetsvc to be cluster aware (both in queries and in the app repository data stored).

[absoludity]

Right now, we can also just assume that any app repository is from the kubeapps cluster (as that's all we support).

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[absoludity]

@antgamdia Just reading the detail of this one, I agree we can close this one given the other issues that are related to it. Even though we aren't using the asset svc any more for this data, we are still using the postgresql db which was the backend to the asset svc. Updating that db table to be cluster aware would be trivial, but the work would be updating the asset-syncer to no longer talk to the DB, but instead talk to an API (of kubeapps APIs), so that it could update the cache from other clusters and other namespaces. But this is already mentioned in #1647.