Qc group dendro cutoffs

[LMBradford]

Adds a quality control step, analogous to the current dendrogram tree height cutoff, but working with trees within each treatment_var group instead of the project as a whole. The config parameter for the within-group trees can be set to null to skip this step and run the QC as normal.

This is helpful for projects where some treatment groups are quite different from the rest in the project, which would cause that group to be considered an outlier in the studywide-tree, even though it really is biologically distinct. In that case, the studywide-tree height cutoff can be loosened, and the group-tree threshold used to remove outliers instead.

[LMBradford]

Merging to main with permission from Matt.