Keep a consumer bound where its data is; only a pin moves it (hq ADR 0232, issue 273)

Issue 258's fix let a mesh seat's holder elsewhere answer before this machine's own provider. Right
for the resolver, which any provider answers alike; for the store's seat it re-bound every database
consumer on a machine running its own store to the holder on another, each was given a fresh, empty
database there, and nothing said so for twenty hours.

- An offer says whether it keeps its consumers' data (`keeps-consumer-data`); unsaid, a provider
  that grants each consumer a credential does. For such a provision the seat's holder no longer
  overrules a provider beside the consumer; a pin still does.
- Where each such consumer was sent is recorded (migration 0071). A resolution that would bind it
  elsewhere keeps the recorded provider and says the move; one whose provider is gone is refused,
  never answered by another.
- A push says a kept move and raises it as an urgent condition at once; the self-check's D12 raises
  it every run, with a pinned move not yet sent as a warning and any unasked move as urgent.

cmd/mesh-controller/sendable.go

@@ -55,6 +55,9 @@ type sendable struct {
 	// was made from — recorded with the send and never on the wire (novox/hq issue 259, ADR 0221).
 	// Composed only on the send path; nil records that it is not known.
 	Builds map[string]string
+	// Bindings is where each consumer of a provision that keeps its data is bound in this declaration
+	// (novox/hq ADR 0232), recorded with the send and never on the wire. Composed only on the send path.
+	Bindings []inventory.Binding
 }
 
 // adoptionEnvelope is what an adopted node is told about its mode. Taken is every module taken on