Keep "nextSequenceToken" from "put_log_events" API call

[spatsatzis]

Keep "nextSequenceToken" from "put_log_events" API call in order to avoid calling "describe_log_streams_with_retries" for a "sequenceToken"

Issue #, if available:
Currently, each time that "flush()" method is called to log data to Amazon CloudWatch a new "describe_log_streams_with_retries()" API call is made to fetch the latest "sequenceToken".

With multiple "Instance Scheduler" solutions in the same AWS account the above behavior might cause throttles for the "DescribeLogStreams" action, the limit is 5 transactions per second (TPS/account/Region) [1]

Description of changes:
With this pull request the "nextSequenceToken" returned by "put_log_events()" method [2] will be stored and re-used in the next "put_log_events()" call in order to avoid calling "describe_log_streams_with_retries" again.

[1] https://docs.aws.amazon.com/AmazonCloudWatch/latest/logs/cloudwatch_limits_cwl.html
[2] https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/logs.html#CloudWatchLogs.Client.put_log_events

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[rakshb]

Thanks for your contribution @spatsatzis. We will review your PR and consider this for a future release