lib/pq library is deprecated

[mdelillo]

Issue

According to their README, the lib/pq library is in maintenance mode. We should instead use pgx.

Diego recently did this here.

[mcwumbly]

text from lib/pq readme:

This package is effectively in maintenance mode and is not actively developed. Small patches and features are only rarely reviewed and merged. We recommend using pgx which is actively maintained.

also (via cloudfoundry/diego-release#511 (comment)), notably, this prevented Diego from removing lib/pq completely, since they also depend on routing-api:

We still had to keep the submodule because routing-api depends on the deprecated library. Opened #164 issue for future reference.

@mdelillo I'm going to label this "scheduled" as well as "help wanted" - we'll pick it up at some point, but if someone out there wants to submit pull requests to resolve this in advance, we would welcome that too.

[mcwumbly]

removing scheduled label from this to better reflect its current priority... if it gets closer to the top of your list again, we'll add it back.

but for now, it's up for grabs!

[moleske]

For giggles I tried deleting the lib/pq submodule and compiling just to see what breaks. It turns out gorm has a dependency on lib/pq since the build failed to compile on tcp router

Failed to compile cf-tcp-router:

../../github.com/jinzhu/gorm/dialects/postgres/postgres.go:7:2: cannot find package "github.com/lib/pq" in any of:
	/usr/local/go/src/github.com/lib/pq (from $GOROOT)
	/routing-release/src/github.com/lib/pq (from $GOPATH)
../../github.com/jinzhu/gorm/dialects/postgres/postgres.go:8:2: cannot find package "github.com/lib/pq/hstore" in any of:
	/usr/local/go/src/github.com/lib/pq/hstore (from $GOROOT)
	/routing-release/src/github.com/lib/pq/hstore (from $GOPATH)

There is a recommended replacement for pq (pgx), but no mention of what to do when pq is a transitive dependencies. I don't have thoughts on this since not super familiar with the code

[mcwumbly]

Looks like maybe we just need to update gorm to the latest version... haven't dug deep, but I think they may have switched underlying libraries now: go-gorm/gorm#1712