Add timestamp support to secondary instance (#10061)

Add timestamp support to secondary instance (#10061)

Summary:
This PR adds timestamp support to the secondary DB instance.

With this, these timestamp related APIs are supported:

ReadOptions.timestamp : read should return the latest data visible to this specified timestamp
Iterator::timestamp() : returns the timestamp associated with the key, value
DB:Get(..., std::string* timestamp) : returns the timestamp associated with the key, value in timestamp

Test plan (on devserver):
```
$COMPILE_WITH_ASAN=1 make -j24 all
$./db_secondary_test --gtest_filter=DBSecondaryTestWithTimestamp*
```

Pull Request resolved: https://github.com/facebook/rocksdb/pull/10061

Reviewed By: riversand963

Differential Revision: D36722915

Pulled By: jowlyzhang

fbshipit-source-id: 644ada39e4e51164a759593478c38285e0c1a666