Use MySqlConnectionStringBuilder instead of 'manually' parsing the connection string

[darraghjones]

I defined my connection string using 'initial catalogue' instead of 'database'. However, this line of code then does not work correctly:
https://github.com/DbUp/DbUp/blob/c8f94a2ff915e651b5b573328e0f01d50d8241c4/src/dbup-mysql/MySqlExtensions.cs#L27

I suggesting using the MySqlConnectionStringBuilder to parse the connection string.

[AdrianJSClark]

I agree, sounds like a great idea.

Happy for you to submit a PR if you have time, @darraghjones. Otherwise someone will have a look as soon as they are free.