based_on tag correctly stores relative paths about bbr

[seth127]

(original post before rewriting as user story)

Summary

The based_on field previously only stored the "model id" a.k.a. the name of the model file without extension. However, this causes collisions when there are nested model directories that have the same file name in them.

Current behavior

The based_on field will store file paths relative to the yaml the field is stored in (still without extensions). This should propogate through to the run_log() output in such a way that the user can trace model ancestry unambiguously.

Possible extension

The run_log tibble (which can be joined easily with log_df <- run_log() %>% add_config()) also contains the model ancestry in the based_on field. This allows establishment of a tree of model ancestry (parents and children of a given model). If a model_ancestry() function is implemented then we could also filter to any children of models that are out-of-date, because those should likely also be re-run.

Decide whether this should be part of this enhancement or should constitute their own separate issue. I think this should be implemented here as well.

[seth127]

I will likely do #77 in tandem with this because if not we will have to circle back and modify this code to look for both yml and yaml files.