Integration of the TTBB Process into the Genproductions Scripts

This merge request integrates the 4F NLOPS implementation of ttbb process into the central gen-production scripts and concludes the work that has been presented on two occasions at the GEN meetings.

Up to now, this important process has been kept outside of the User-Processes-RES, and only accessible through an external repository created by the original authors of the program. Because of this, in Run 2, the simulation of this process relied on pLHE events being produced by specific analysis groups needing the sample. To overcome this complication for Run 3, a first initial set of gridpacks was developed for this process using a private setup for their creation (see first presentation). As a follow-up, an effort to find an alternative workflow to have the process embedded in the gen-production scripts has been made, which led to the proposed implementation detailed in this merge request. This approach exploits the usage of Powheg local sources within the central gen-production system to have prepared the resources/code needed for ttbb, in such a way as to just have it copied over and executed without extra fixes. Some additions are introduced in the scripts to handle the newer required version of OpenLoops. These details were discussed in the second presentation recently, where validation results were also shown.

In another merge request to the gen-production cards repository, a set of input cards corresponding to the three relevant channels will be added.