Allow client to reconnect when specified

[josevalim]

No description provided.

[josevalim]

@greg-rychlewski here are the changes. The idea is that, when PostgresSQL detects the connection was dropped, we can now return :disconnect_and_retry. However, notice we cannot always do this, as a connection may drop in the middleware of a query, and we could retry something dangerous. Therefore, we can only emit retry when preparing/binding queries or issuing begin statements and so on. I am starting with a checkout retries of 3 but for the Neon case we may want to set it to the pool size + 1.

[josevalim]

💚 💙 💜 💛 ❤️

[greg-rychlewski]

@josevalim beautiful :)

I could do the Postgrex side unless you already started/want to?

[josevalim]

@greg-rychlewski please go ahead if you want to! I can probably focus on this again only next wednesday!