rebase: bump google.golang.org/grpc from 1.50.1 to 1.51.0

Bumps [google.golang.org/grpc](https://github.com/grpc/grpc-go) from 1.50.1 to 1.51.0.
- [Release notes](https://github.com/grpc/grpc-go/releases)
- [Commits](https://github.com/grpc/grpc-go/compare/v1.50.1...v1.51.0)

---
updated-dependencies:
- dependency-name: google.golang.org/grpc
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

vendor/google.golang.org/grpc/balancer/balancer.go

@@ -110,6 +110,11 @@ type SubConn interface {
 	UpdateAddresses([]resolver.Address)
 	// Connect starts the connecting for this SubConn.
 	Connect()
+	// GetOrBuildProducer returns a reference to the existing Producer for this
+	// ProducerBuilder in this SubConn, or, if one does not currently exist,
+	// creates a new one and returns it.  Returns a close function which must
+	// be called when the Producer is no longer needed.
+	GetOrBuildProducer(ProducerBuilder) (p Producer, close func())
 }
 
 // NewSubConnOptions contains options to create new SubConn.
@@ -371,3 +376,21 @@ type ClientConnState struct {
 // ErrBadResolverState may be returned by UpdateClientConnState to indicate a
 // problem with the provided name resolver data.
 var ErrBadResolverState = errors.New("bad resolver state")
+
+// A ProducerBuilder is a simple constructor for a Producer.  It is used by the
+// SubConn to create producers when needed.
+type ProducerBuilder interface {
+	// Build creates a Producer.  The first parameter is always a
+	// grpc.ClientConnInterface (a type to allow creating RPCs/streams on the
+	// associated SubConn), but is declared as interface{} to avoid a
+	// dependency cycle.  Should also return a close function that will be
+	// called when all references to the Producer have been given up.
+	Build(grpcClientConnInterface interface{}) (p Producer, close func())
+}
+
+// A Producer is a type shared among potentially many consumers.  It is
+// associated with a SubConn, and an implementation will typically contain
+// other methods to provide additional functionality, e.g. configuration or
+// subscription registration.
+type Producer interface {
+}

vendor/google.golang.org/grpc/balancer/base/balancer.go

@@ -157,8 +157,8 @@ func (b *baseBalancer) mergeErrors() error {
 
 // regeneratePicker takes a snapshot of the balancer, and generates a picker
 // from it. The picker is
-//  - errPicker if the balancer is in TransientFailure,
-//  - built by the pickerBuilder with all READY SubConns otherwise.
+//   - errPicker if the balancer is in TransientFailure,
+//   - built by the pickerBuilder with all READY SubConns otherwise.
 func (b *baseBalancer) regeneratePicker() {
 	if b.state == connectivity.TransientFailure {
 		b.picker = NewErrPicker(b.mergeErrors())

vendor/google.golang.org/grpc/balancer/conn_state_evaluator.go

@@ -34,10 +34,10 @@ type ConnectivityStateEvaluator struct {
 // RecordTransition records state change happening in subConn and based on that
 // it evaluates what aggregated state should be.
 //
-//  - If at least one SubConn in Ready, the aggregated state is Ready;
-//  - Else if at least one SubConn in Connecting, the aggregated state is Connecting;
-//  - Else if at least one SubConn is Idle, the aggregated state is Idle;
-//  - Else if at least one SubConn is TransientFailure (or there are no SubConns), the aggregated state is Transient Failure.
+//   - If at least one SubConn in Ready, the aggregated state is Ready;
+//   - Else if at least one SubConn in Connecting, the aggregated state is Connecting;
+//   - Else if at least one SubConn is Idle, the aggregated state is Idle;
+//   - Else if at least one SubConn is TransientFailure (or there are no SubConns), the aggregated state is Transient Failure.
 //
 // Shutdown is not considered.
 func (cse *ConnectivityStateEvaluator) RecordTransition(oldState, newState connectivity.State) connectivity.State {
@@ -55,7 +55,11 @@ func (cse *ConnectivityStateEvaluator) RecordTransition(oldState, newState conne
 			cse.numIdle += updateVal
 		}
 	}
+	return cse.CurrentState()
+}
 
+// CurrentState returns the current aggregate conn state by evaluating the counters
+func (cse *ConnectivityStateEvaluator) CurrentState() connectivity.State {
 	// Evaluate.
 	if cse.numReady > 0 {
 		return connectivity.Ready