ENHANCEMENT: Passing pooled treatment groups into TLG

[barnett11]

Users are used to customisable treatment groupings/poolings in their TLGs - an example would be All Active arm to pool active treatment groups against Placebo. How can we apply in chevron, currently we only have overall total pooling?

[clarkliming]

We can handle that in preprocessings to group multiple treatment arms into 'all active'; the logic using rtables to add poolings is a bit different from what we are using now and it can be difficult to harmonize