Filter by repostiories for Carvel plugin

[antgamdia]

Summary
Currently, the "filter by repo" is not working* for carvel packages as we aren't really using this filter:

kubeapps/cmd/kubeapps-apis/plugins/kapp_controller/packages/v1alpha1/server_utils.go

Lines 280 to 285 in f298db6

	func FilterMetadatas(metadatas []*datapackagingv1alpha1.PackageMetadata, filterOptions *corev1.FilterOptions) []*datapackagingv1alpha1.PackageMetadata {
	// Currently we support filtering by query or category but not by repository
	// (UX doesn't yet display carvel repo in filter options).
	// Once the UX does, we should be able to filter by repository
	// also as its now an annotation:
	// https://github.com/vmware-tanzu/carvel-kapp-controller/pull/532

(*) from a backend PoV, the UI is actually filtering, but from the whole list of packages.

Background and rationale
Once Carvel repos can be added via the UI we should support filtering by repos also in this plugin.

Description
Allow filtering by repo in carvel packages.

Acceptance criteria

• The "filter by repos" is implemented in the plugin backend.

Additional context
Not critical as, feature-wise, it is actually working with the UI workaround.