No way of configuring a MySQL socket

We should allow the configuration of a database socket. The configuration key for this is `unix_socket`. I propose to identify when during the wizard a value prepended by `/` is entered we will automatically assume a socket connection and fill the `unix_socket` configuration key.

Start by locating the database-connection wizard and its handling of MySQL inputs, then search for the unix_socket configuration key and existing connection options. Done means a value beginning with / is treated as a socket connection and populates unix_socket.

Written by the indexing model from the issue text.