wip: docs metrics start
metrics documentation changes, changed history endpoint to runs, gauge example, querying by run-id
update to docs based on code review comments
Wrap intialize and destroy methods of HttpSerivceHandler in txExecutor
Moving keys and values to constants
Missed one
code review comments
change based on review comments
Spark Integration: Added support for custom user metrics in Spark
Spark Integration: Modified SparkMetricsTest to support custom metrics test
Spark Integration: SparkPageRank example emits custom metrics
fixed deleting metrics upon redeployment of changed app
Small doc changes
PR comment
Merge pull request #718 from caskdata/feature/spark-custom-metrics

Spark Integration: Custom User Metrics
Merge pull request #715 from caskdata/feature/service-methods-tx-fix

CDAP-754 : Wrap initialize and destroy methods of HttpSerivceHandler in txExecutor
Getting datasets inside transactions for service workers is synchronized
Merge pull request #725 from caskdata/feature/worker-synchronized-get-dataset

Synchronize getDatasets for workers
use incrmenet and gauge in mr metrics
add json serializer to not send endTime if status is Running for programs