Add initSQLFilePath option

[Sebastian-Webster]

Like the initSQLString option, but instead of providing a SQL string, you can provide a file path to a .sql file.

The order of operations for the init file that the MySQL Server will use to initialise will be (first - last):

1. mysql-memory-server internal SQL operations (for things like setting user username and creating initial database)
2. initSQLString option
3. New initSQLFilePath option

If there is an error reading the initSQLFilePath file when a value is provided for that option, an error should be thrown and the database should not be started.