Default types replaced with pgtype wherever possible

[Amogh-Bharadwaj]

Also set connection pool limit to 3 for our postgres client

[serprex]

What's the benefit of this? It seems like an unnecessary intermediary compared to using go's primitive types

jackc/pgtype#44 seems to give some perspective, but wanting to know experience on our end

[iskakaushik]

@serprex the reason was null handling is handled better with these types. When scanning a null string, we encountered an NPE. So pre-emptively moving to this. It might make more sense to inspect each call to see if the extra type is needed, but given that most of these calls are to secondary to mirror perf, I am inclined to be ok with using these types.

[serprex]

should explain more in PR description so information is in git history