feat(mysql): allow to connect with mysql driver without default behavor

[darkecho731]

Hi, I ran into some issues connecting with a MariaDB Instance behind ProxySQL (I would guess, that the Variables are not replicated correctly to the cluster).

I don't have any access to the Database or the Logs and thus can't debug that much but found out, that the only differences to other MySQL Drivers are the Parameters set after connecting to the Instance.

I have found this Issue #2389 and after hacking around a bit, I found that turning off the initialization "fixes" my problem.

This PR gives an option to disable the Default Behavior after connecting. I haven't touched the defaults, so there should be no breaking behavior.

[abonander]

My disposition is still the same as in #2389 (comment)

I'd prefer to add toggles/setters for the individual options, because the defaults all have specific reasons for existing.

[darkecho731]

You're right, that's probably more sensitive.

I have implemented the setters (although I'm not 100% convinced about the naming) and adapted the connection behavior accordingly (although I'm using more Heap allocations to gain better readability, but I can change that to a single String again, if that is preferred).

The comment above the old implementation mentions setting the NO_ZERO_DATE and NO_ZERO_IN_DATE variables but I haven't added settings for them, as they are not added in the actual implementation.

[abonander]

One documentation change and one API change.

[darkecho731]

Thanks. I have updated the set_timezone_utc to a timezone setter and adopted the documentation improvements.

Edit: the impl Option<String> may be changed to impl Option<impl Display> to allow Some("+01:00") to be used but it's probably better to make it explicit, to prevent passing an integer or something.

Edit2: maybe impl Option<impl Into<String>>

[abonander]

I'm happy with this as it is.