Enabling ShardIndexingPressureMetricsCollector by default

[psychbot]

We want to enable the ShardIndexingPressure Collector to be enabled by default.

These are scenarios which we have tested and have positive result from code perspective -

1. ShardIndexingPressure enabled and Collector enabled - Will collect metrics.
2. ShardIndexingPressure disabled and Collector enabled - Will not collect metrics.
3. ShardIndexingPressure enabled/disabled and and Collector disabled - Will not collect metrics.

ShardIndexingPressure feature can be toggled as per the need and it will take affect in PA as the collector is enabled by default.
Also we have the andon cord to disable this collector in case something goes really wrong
Chances of things going wrong is really low because of below reasons -

1. This collector will be added to the scheduled metrics collector only when the ShardIndexingPressure class is present in the code.
2. This collector will process only 50 elements from hot objects - Adding a additional check to just process first 50 objects of hot store performance-analyzer#284
3. This feature is available for newer versions.