Add a mechanism to create process dependencies

Sometimes a process will require that a process has been placed previously inside the data chain. Then, it would be interesting to introduce a mechanism to indicate those dependencies inside the process.

We could think of something like inserting a line of code as follows in our process:

// Values 1 or 2 define if the process is to be recommended or required. It could be an enum giving better legibility to the code.
ProcessRequired("TRestMyRecommendedProcess", 1);
ProcessRequired("TRestMyRequiredProcess", 2);

or

ProcessRecommended("TRestMyRecommendedProcess");
ProcessRequired("TRestMyRequiredProcess");

or

AddProcessDependency("TRestMyRecommendedProcess", 1);
AddProcessDependency("TRestMyRequiredProcess", 2);

Then, the processing will warn in case of a recommended process is not present, or prompt an error in case a required process is not available.

@rest-for-physics/core_dev

The issue names no files or tests. Start by tracing where processing checks process availability in the data chain, then clarify how recommended dependencies should warn and required dependencies should error. Done means the dependency API and both behaviors are agreed and specified.