In PMM1 we had a flag '--create-user' for 'pmm-admin add mysql' command
PMM2 doesn't have this flag working as for now, but it's absence confuses people.
Proposed solution :
- This must not lead to adding Service with root:root credentials, this is no what user expects
- --create-user flag should be not visible on `pmm-admin add mysql --help` command
- Full feature implementation in PMM-4776