feat: add documentation for partition value limit

BREAKING CHANGE: make the client library gRPC only

PiperOrigin-RevId: 666551276

Source-Link: googleapis/googleapis@6f3c628

Source-Link: googleapis/googleapis-gen@9c59969
Copy-Tag: eyJwIjoiLmdpdGh1Yi8uT3dsQm90LnlhbWwiLCJoIjoiOWM1OTk2OThmOTBhZTU2YTYxZTM4YTI2NmJkNzcwNTYxNGM1ZGZmNiJ9

owl-bot-staging/v1alpha/google/cloud/bigquery_storage_v1alpha/types/partition.py

@@ -147,7 +147,8 @@ class MetastorePartition(proto.Message):
             Required. Represents the values of the
             partition keys, where each value corresponds to
             a specific partition key in the order in which
-            the keys are defined.
+            the keys are defined. Each value is limited to
+            1024 characters.
         create_time (google.protobuf.timestamp_pb2.Timestamp):
             Output only. The creation time of the
             partition.