Implement resource evaluation for pre_rocket feature

Related to Issue87 of the vre-middleware project:

The qadapter's pre_rocket keyword is particularly important for batch type nodes and HPC resources, as it allows actions such as setting up environment variables, activating virtual environments, and loading modules. Independent of whether a user employs a custom, or default (from resconfig module) qadapter, the pre_rocket keyword should be supported.

One possible schema for the pre_rocket resources can be found here. The actual evaluation of these requested resources should be implemented in the VRE-Language package.