Fix: Support for max event size limit

[amandas-sukionis]

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
  Fix/Feature: Adds handling of max event size of 256 KB https://docs.aws.amazon.com/AmazonCloudWatch/latest/logs/cloudwatch_limits_cwl.html

• What is the current behavior? (You can also link to an open issue here)
  Currently, if a large message (256 KB or larger) is being logged, there is a Aws\CloudWatchLogs\Exception\CloudWatchLogsException runtime exception thrown with a message similar to "Log event too large: 524256 bytes exceeds limit of 262144"}" which if unhandled breaks code execution.

• What is the new behavior (if this is a feature change)?
  With the new behavior the message is split into smaller chunks and logged as separate events. It does simply cut the string at the limit size.

• Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)
  No.

• Other information:
  None.

[maxbanton]

Hi @amandas-sukionis. Thanks for your pull request. Could you please explain use cases when you need to put 524256 bytes of log message?

[amandas-sukionis]

Sure, we are relying on a 3rd party XML api to manage user bookings and on the error cases we log the full request/response information. Due to the nature of these requests they are pretty large. This is not a very common case for us, but it still happens. It seemed that it would be easier to implement this on the library level (as it's an AWS limit, similar to batch size) instead of managing log sizes and error handling on our part.

[maxbanton]

Thanks @amandas-sukionis. Merged and new version published https://packagist.org/packages/maxbanton/cwh#v1.1.9