Add MasterThrottlingMetric Collector

[dhwanilpatel]

Description of changes:

Code change is for Master Throttling of Pending task. It will publish two metric 1) Total throttled tasks at master node 2) Number of task on which data node is actively retrying. This feature is yet to be contributed to Opensource ES. I have added the check for availability of this feature in collector so building with or without this feature will pass. If this feature is not available then collector will simply return.

Testing

1. /gradlew test Successful
2. Tested in test domain by replacing JAR.

Tmp file

^master_throttling_metrics
{"current_time":1602617137529}
{"Data_RetryingPendingTasksCount":0,"Master_ThrottledPendingTasksCount":0}$

Verified metric from table

sqlite> select * from Master_ThrottledPendingTasksCount;
0.0|0.0|0.0|0.0

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[yojs]

This looks good to me. We just need an API to be able to turn this collector off and this should be turned off by default for the next release.

[adityaj1107]

Merged by mistake: Merged a revert PR: #221