WMAgent: Retire obsolate Mysql prefixes for the agent deployment initialization and management scripts

[todor-ivanov]

Impact of the new feature
WMAgent

Is your feature request related to a problem? Please describe.
This Feature is a must for us once we decide to migrate to the latest MariaDB 11.0. Since version 10.11 MariaDB stopped supporting the soft links created to the current program executables prefixing them with the already obsolete myqsl* prefixes: https://mariadb.com/kb/en/mariadb-11-0-1-release-notes/#packaging

This triggers a command renaming campaign in our client script which needs to happen before

Describe the solution you'd like
WE have to rename all commands and variables following the convention:

• Any name which relates to mysql (the client or the database as a whole) - shifts to mariadb
• Any name which relates to mysqld (the daemon running the databsae) - shifts to mariadbd

Describe alternatives you've considered
None. It is a must do

Additional context
None

Part of the following meta issue: #11314

[todor-ivanov]

FYI: @amaltaro