feat(bigtable): lower the value for max rpc channels as channel resize is slow (1m, 2 channel) (#2656)

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Author: sushanb

google-cloud-bigtable/src/main/java/com/google/cloud/bigtable/data/v2/stub/EnhancedBigtableStubSettings.java

@@ -446,7 +446,9 @@ public static InstantiatingGrpcChannelProvider.Builder defaultGrpcTransportProvi
  ChannelPoolSettings.builder()
  .setInitialChannelCount(10)
  .setMinRpcsPerChannel(1)
- .setMaxRpcsPerChannel(50)
+ // Keep it conservative as we scale the channel size every 1min
+ // and delta is 2 channels.
+ .setMaxRpcsPerChannel(25)
  .setPreemptiveRefreshEnabled(true)
  .build())
  .setMaxInboundMessageSize(MAX_MESSAGE_SIZE)