R1:1ecfa0313c48

Add a `./bin/storage shell` command

Summary: Fixes T7078. Adds a `./bin/storage shell` command which passes through to a MySQL shell. This is slightly more convenient than running `mysql` manually.

Test Plan: Ran `./bin/storage shell` and got a MySQL shell.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: Korvin, epriestley

Maniphest Tasks: T7078

Differential Revision: https://secure.phabricator.com/D11548