[docdb][ysql] Provide follower reads through YSQL

[bmatican]

One option we were discussion, that might be cheap to do, would be to retrofit some isolation level, such as READ_COMMITTED to signal this.

[jameshartig]

I also think it might be good to explore the use of connection string params like how azure does it: https://docs.microsoft.com/en-us/azure/azure-sql/database/read-scale-out

[RaidAndFade]

Just writing to note that this is something I am deeply interested in, hopefully it comes soon.

[m-iancu]

Fixed by 5ee5764.