[DOC] Add a new request field to segment replication backpressure

[Poojita-Raj]

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Tell us about your request. Provide a summary of the request and all versions that are affected.
There's a list of fields for segment replication backpressure listed in this doc:
https://opensearch.org/docs/latest/tuning-your-cluster/availability-and-recovery/segment-replication/backpressure/#request-fields

We need to add a new field here:

Field	Data type	Description
SEGMENT_REPLICATION_INDEXING_PRESSURE_ENABLED	Boolean	Enables the segment replication backpressure mechanism. Default is false.
MAX_REPLICATION_TIME_BACKPRESSURE_SETTING	Time unit	The maximum amount of time that a replica shard can take to copy from the primary shard. Once MAX_REPLICATION_TIME_BACKPRESSURE_SETTING is breached along with MAX_INDEXING_CHECKPOINTS, the segment replication backpressure mechanism is initiated on primary. Default is 5 minutes.
MAX_REPLICATION_LIMIT_STALE_REPLICA_SETTING	Time Unit	The maximum amount of time that a replica shard can take to copy from the primary shard. Once MAX_REPLICATION_LIMIT_STALE_REPLICA_SETTING is breached, we start failing the replica shard. Default is 0 minutes(disabled).
MAX_INDEXING_CHECKPOINTS	Integer	The maximum number of indexing checkpoints that a replica shard can fall behind when copying from primary. Once MAX_INDEXING_CHECKPOINTS is breached along with MAX_REPLICATION_TIME_BACKPRESSURE_SETTING, the segment replication backpressure mechanism is initiated. Default is 4 checkpoints.
MAX_ALLOWED_STALE_SHARDS	Floating point	The maximum number of stale replica shards that can exist in a replication group. Once MAX_ALLOWED_STALE_SHARDS is breached, the segment replication backpressure mechanism is initiated. Default is .5, which is 50% of a replication group.

What other resources are available? Provide links to related issues, POCs, steps for testing, etc.
opensearch-project/OpenSearch#9507
opensearch-project/OpenSearch#8453

[hdhalter]

@Naarcha-AWS - Is this complete? Can we close?

[hdhalter]

@Naarcha-AWS - It doesn't look like this was done in 2.10. Can we get these added? Thanks.