Use LogSplit for logs exceeding maximum size

[rafal-dudek]

Is your feature request related to a problem? Please describe.
In our projects we are using LoggingAppender to write logs in GKE. Some of the logs are bigger than the limit and they are rejected:
ERROR: onFailure exception: com.google.cloud.logging.LoggingException: io.grpc.StatusRuntimeException: INVALID_ARGUMENT: Log entry with size 293.5K exceeds maximum size of 256.0K

Describe the solution you'd like
LoggingAppender should split the logs exceeding limit and use "split" field described in google.logging.v2 API.

Additional context
LogEntry definition with split field:
https://cloud.google.com/logging/docs/reference/v2/rpc/google.logging.v2#logentry
LogSplit definition:
https://cloud.google.com/logging/docs/reference/v2/rpc/google.logging.v2#google.logging.v2.LogSplit
Field definition in proto file:
https://github.com/googleapis/googleapis/blob/master/google/logging/v2/log_entry.proto#L183