create a dedicate path variable to isolate where look for .maxctrl.cnf

this is really important for a customer case.

When .maxctrl.cnf is used, maxscale look for that file only on $HOME/.maxctrl.cnf

with more configurations that isolated different maxscales services on the same instance, the maxctrl.cnf become a limitation.

we need to be able to isolated for single maxscale service where maxsacle will lookg for .maxctrl.cnf

as spoken with markus i think the best is add

[maxctrl] session inside the .cnf
credential_path=/my/isolated/path_for

no system [maxctrl] and no symlink , the path need to be attach to the spedici configuration of a specific maxscale

in this way you can start different maxscales on the same linux instance and have different credential for each, without anything to add outside of maxscale itself