Bring a cell's hold back and alert while its location is unresolved #835

A cell that cannot name its location waits for one, and two things do not follow that wait. ecv raised them in the review of #833, with a third, smaller one.

Proposed scope

• The hold's watch drops an interface event while the location is unresolved, and nothing requeues it. A hold waiting on that interface's removal stays until the context next gets an event. Requeue the dropped event, or watch ServingLocation.
• No alert reads nso_cell_location_identity_waiting. Neither NSO's rules nor infra name it today. Add a warning for a cell that waits.
• The description of the locations-crds task in Taskfile.test-infra.yml still says cells read the ServingLocation downstream. The e2e env applies it upstream, where the cell runs.

Acceptance criteria

• A hold waiting on an interface that went while the location was unresolved is released once the location resolves
• In promtool tests, a cell waiting on its location raises one warning, and a cell that resolves raises none
• The task's description names the cluster the cell reads

Related to #664