Add guidance on time to resynchronize PostgreSQL on Geo secondary
Summary
When a customer with a Geo secondary is upgrading PostgreSQL, they currently need to resynchronize the PostgreSQL database on the secondary after the upgrade. For larger customers, this can take hours or even days.
Proposal
We note the requirement to resynchronize on the database upgrade page, and we note that this can't be done without downtime, but it isn't obvious that this could be hours of downtime. The downtime will depend on the size of the database and the speed of the connection to the secondary, so it is difficult to say how much downtime it will take. However, to help customers prepare for the upgrade, could we provide an example of how long this will take? For example, "Keep in mind that at a connection speed of x, and a database size of x GB, resynchronization could take approximately x hours". As the documentation stands today, it feels like we gloss over this a bit.