Add fullyQualifiedUsername to MySQLUser secret

[kyschouv]

Describe the current behavior MySQLServer secrets include a fullyQualifiedUsername value. MySQLUser secrets do not, and the value must be created by combining the username with the mySqlServerName. It would be nice to not have to do that, especially as it can be difficult to compose and apply depending on the usage (e.g. a Helm chart may not be set up to define environment variables for username and server name and then later combine them into a fully qualified user name).

Describe the improvement Add fullyQualifiedUsername to the secret generated for a MySQLUser.

[theunrepentantgeek]

v1 is in maintenance mode, so we won't be making a change there.

However, we need to be aware of this issue for v2, as we need to avoid replicating the problem there.

[matthchr]

Somewhat related to #2555

[matthchr]

Closing this in favor of the more generic #2555. That issue may not be solved for a little while yet (we need to think about it), so if there's an explicit need for this field or one like it on an ASOv2 resource feel free to open a new issue for that and we may be able to action that specific one.