Please add mysql operator support for MySQL 8.0

[sjmudd]

This is a feature request

• MySQL 8.0 is the latest GA version of MySQL and has been that way for a couple of years so it would be good to provide examples with the latest version, and comment if it works on "older versions", e.g. 5.7, 5.6, 5.5, ....
• I see from mysql-operator #314 that there are already reported issues of confusion with helm2/helm3. It would be good to fix and document these to make life easier for people who want to try out these recipes.
• I am also under the impression that these recipes are not "official" from the MySQL teams. If that's the case it would be good to make this clearer as I guess you work for Oracle and some people may see this to be an official operator from the MySQL team, given MySQL is part of Oracle. A tiny clarification at the top of this repo would be really helpful as not everyone may be aware they can find official MySQL information under https://github.com/mysql/, even if at the moment that does not include any MySQL operators for Kubernetes.

What happened?

I tried to follow the tutorial and things didn't work "out of the box", partly due to the helm2/helm3 issue and because I'd like to use a MySQL 8.0 container.

What you expected to happen?

I would expect the instructions to work for 8.0 with helm3 and mention using older versions of helm or MySQL.