List Label Resource Mappings by Label Names and or Label IDs via label service

Proposal:
The ability to list resources associated to a label via the label names or label ids.

type LabelService interface {
    ... existing
    AssociatedResources(ctx context.Context, filter LabelAssociationFilter) ([]LabelResourceMapping, error)
}

type LabelAssociationFilter struct {
    ResourceType ResourceType // optional

    OrgID ID    

    // at least 1 entry for 1 of the following
    IDs []ID
    Names []string
}

Current behavior:
Forces the API consumer to make multiple hops here to find this.

Desired behavior:
Remove the work arounds, multiple http calls and make the label service encapsulate this behavior.

Alternatives considered:
The existing painful experience

Use case:
This is super helpful for finding resources by a label. Say the CLi wants to limit resources in teh list calls by a label. Or the UI wants to find all resources for a given label. These are useful for finding meaningful context for resources.

Start at the LabelService interface and trace the current multiple-hop lookup described in the issue. Define the service behavior around AssociatedResources and LabelAssociationFilter, including IDs, names, organization, and optional resource type. Done means consumers can find associated resources through the label service without multiple HTTP calls.