Fix setting maxInboundMetadataSize from GLOBAL

[o-shevchenko]

maxInboundMetadataSize works as expected after #1064 if you set it for the needed channel.
But it was missed for GLOBAL in copyDefaultsFrom method

grpc:
  client:
    GLOBAL:
      max-inbound-metadata-size: 16384 # value here is not copied to other services
    service:
      address: service:6565
      max-inbound-metadata-size: 16384 # you have to specify value for service even it's already present for  GLOBAL
      ```