Call `app` at start of every pg method

Fixes #943 , poorly :(

I tried adding an `initialize` method to set this up prior to any method, but it made all the tests fail because they don't specify `-a` :frowning: 


```shell
~ ❯ heroku pg:info
 !    Internal server error.
 !    Run `heroku status` to check for known platform issues.

~ ❯ ./Projects/Heroku/heroku/bin/heroku pg:info                                                                                                                                   
 !    No app specified.
 !    Run this command from an app folder or specify which app to use with --app APP.

~ ❯ ./Projects/Heroku/heroku/bin/heroku pg:info -a test-thing                                                                                                                     === HEROKU_POSTGRESQL_OLIVE_URL (DATABASE_URL)
Plan:        Standard Yanari
[...]
```