adding MaxClientsVHost for apache templates

[vincib]

http://mpm-itk.sesse.net/ says :

MaxClientsVHost: A separate MaxClients for the vhost. This can be useful if, say, half of your vhosts depend on some NFS server; if the NFS server goes down, you do not want the children waiting forever on NFS to take the non-NFS-dependent hosts down. This can thus act as a safety measure, giving “server too busy” on the NFS-dependent vhosts while keeping the other ones happily running. (Of course, you could use it to simply keep one site from eating way too much resources, but there are probably better ways of doing that.)

AlternC used to have this in the vhost configuration file for apache (with a limit of 40)

we should add those to the FPM configuration templates for apache too