[Timestamp Pinning in Remote Store] Pinned timestamp service to pin/unpin timestamp

[sachinpkale]

Is your feature request related to a problem? Please describe

As part of #15057, we are introducing support of timestamp pinning for remote backed storage feature.

Describe the solution you'd like

The service will provide following 2 APIs:

1. pinTimestamp(long timestamp, String pinningEntity)
2. unpinTimestamp(long timestamp, String pinningEntity)

Related component

Storage:Remote