Migtate transcoder's sql to sqlc + pgx

[zoriya]

sqlc has a way better DX (just look at the auth code).
pgx also has some goodies (like supporting sslmode=prefer so we don't have #750)

[felipemarinho97]

This is just my opinion, but I would prefer the transcoder application not to use ORM or any wrapper to access the database, I think it only makes the project more complex.

My last contribution to add new tags to subtitles was simple because it didn't require learning any new technology or paradigm. I simply wrote migrations and adapted SQL code as simple as I would do in any other Go project.

Keep things as simple as possible, it's the Go way of doing things :)

A little copying is better than a little dependency.

I suggest using just pgx alone, it's a great driver