[Resiliency] Enable guard rails by default

[gbbafna]

Describe the bug

We have added three systems to protect the cluster from browning it out .

1. Shard Indexing Backpressure -
2. Search Backpressure - [RFC] Backpressure in Search Path #1329
3. Cluster Manager Throttling - Cluster Manager Task Throttling #479

These are disabled by default. It puts the onus users to enable it. Most of them will be unaware of these and will lead to cluster instability .

Expected behavior

All these features should be enabled by default. We can set the default thresholds on a higher side to make this change safer .

[shwetathareja]

+1 @gbbafna to enable these by default with reasonable thresholds.