Add a test volume pipeline for specific cases

The goal is to be able to launch the test volume on a specific server, typically a preprod of a customer to validate things.

A copy of the current test_volume.groovy will be done with following changes:

• custom server URL
• custom user, already existant
• custom workspace to use for document creations
• custom number of agents to use*
• no local Nuxeo instance required

* We are currently using one agent by OS (GNU/Linux, macOS and Windows), but we could try to use more (we are several agents by OS, use them!).

When that pipleline script will be ready, a new job will be created on the QA/CI.