rebase: bump google.golang.org/grpc from 1.49.0 to 1.50.1

Bumps [google.golang.org/grpc](https://github.com/grpc/grpc-go) from 1.49.0 to 1.50.1.
- [Release notes](https://github.com/grpc/grpc-go/releases)
- [Commits](https://github.com/grpc/grpc-go/compare/v1.49.0...v1.50.1)

---
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/metadata/metadata.go

@@ -50,7 +50,7 @@ type MD map[string][]string
 // Keys beginning with "grpc-" are reserved for grpc-internal use only and may
 // result in errors if set in metadata.
 func New(m map[string]string) MD {
-	md := MD{}
+	md := make(MD, len(m))
 	for k, val := range m {
 		key := strings.ToLower(k)
 		md[key] = append(md[key], val)
@@ -74,7 +74,7 @@ func Pairs(kv ...string) MD {
 	if len(kv)%2 == 1 {
 		panic(fmt.Sprintf("metadata: Pairs got the odd number of input pairs for metadata: %d", len(kv)))
 	}
-	md := MD{}
+	md := make(MD, len(kv)/2)
 	for i := 0; i < len(kv); i += 2 {
 		key := strings.ToLower(kv[i])
 		md[key] = append(md[key], kv[i+1])
@@ -182,19 +182,51 @@ func FromIncomingContext(ctx context.Context) (MD, bool) {
 	if !ok {
 		return nil, false
 	}
-	out := MD{}
+	out := make(MD, len(md))
 	for k, v := range md {
 		// We need to manually convert all keys to lower case, because MD is a
 		// map, and there's no guarantee that the MD attached to the context is
 		// created using our helper functions.
 		key := strings.ToLower(k)
-		s := make([]string, len(v))
-		copy(s, v)
-		out[key] = s
+		out[key] = copyOf(v)
 	}
 	return out, true
 }
 
+// ValueFromIncomingContext returns the metadata value corresponding to the metadata
+// key from the incoming metadata if it exists. Key must be lower-case.
+//
+// Experimental
+//
+// Notice: This API is EXPERIMENTAL and may be changed or removed in a
+// later release.
+func ValueFromIncomingContext(ctx context.Context, key string) []string {
+	md, ok := ctx.Value(mdIncomingKey{}).(MD)
+	if !ok {
+		return nil
+	}
+
+	if v, ok := md[key]; ok {
+		return copyOf(v)
+	}
+	for k, v := range md {
+		// We need to manually convert all keys to lower case, because MD is a
+		// map, and there's no guarantee that the MD attached to the context is
+		// created using our helper functions.
+		if strings.ToLower(k) == key {
+			return copyOf(v)
+		}
+	}
+	return nil
+}
+
+// the returned slice must not be modified in place
+func copyOf(v []string) []string {
+	vals := make([]string, len(v))
+	copy(vals, v)
+	return vals
+}
+
 // FromOutgoingContextRaw returns the un-merged, intermediary contents of rawMD.
 //
 // Remember to perform strings.ToLower on the keys, for both the returned MD (MD
@@ -222,15 +254,18 @@ func FromOutgoingContext(ctx context.Context) (MD, bool) {
 		return nil, false
 	}
 
-	out := MD{}
+	mdSize := len(raw.md)
+	for i := range raw.added {
+		mdSize += len(raw.added[i]) / 2
+	}
+
+	out := make(MD, mdSize)
 	for k, v := range raw.md {
 		// We need to manually convert all keys to lower case, because MD is a
 		// map, and there's no guarantee that the MD attached to the context is
 		// created using our helper functions.
 		key := strings.ToLower(k)
-		s := make([]string, len(v))
-		copy(s, v)
-		out[key] = s
+		out[key] = copyOf(v)
 	}
 	for _, added := range raw.added {
 		if len(added)%2 == 1 {