New PF4 UI : Change "Directory path" by "Server" path to remark that folder must be on the server host

I find confusing the term "Directory path" because it might be understood that the folder to fetch applications resides on the client-side host but in fact, the folder resides in the server host. It might not be important if MTA is deployed and used in the same host, but it makes a difference when MTA is deployed in HOST_1 and the user access MTA through the network.

The Patternfly 3 version uses "Server path" too.