Make flag CLIENT_FOUND_ROWS configurable per user

[renecannao]

This is an improvement over #445 .
In #445 , a new global variable mysql-client_found_rows was added, and it defaults to true to work with ORM likes SQLAlchemy and django .

ProxySQL can be more granular and have CLIENT_FOUND_ROWS enabled or disabled on a per user basis.

Note: according to the documentation, COM_CHANGE_USER doesn't allow to change capabilities, therefore CLIENT_FOUND_ROWS cannot be changed on an already established connection.
To implement this feature, we first need to enhance the connection pool in order to try to find a connection with the closest attributes possible, like for example same user.

[renecannao]

Closing because fixed