[Plugins] Write a Rails gem to make their prepared statements work

[levkk]

This is not strictly PgDog-related.

Rails (Ruby on Rails) does a lot of nasty stuff with prepared statements that make them basically unusable:

1. It uses IN ($1, $2, $3) instead of = ANY($1)
2. It injects comments directly into the query sql

Both blows up the statement cache cardinality, on our end and theirs.

We should write a gem that monkeypatches this so people have an easier time migrating to prepared statements when using Rails. We should support several recent versions.