Rename ComponentSelector to DecisionTree

[tsalo]

Summary

This stems from #969. Now that the ComponentSelector's tree config also determines which metrics should be calculated, the name is somewhat misleading. It might make sense to rename it to DecisionTree.

[handwerkerd]

With the way we're currently using nomenclature, "Decision Tree" are the steps in the process for deciding while "Selector" is the processing the does several things including validating and running the decision tree. Calling the selector "decision tree" is using a more narrow rather than a broader term.

The in-progress change is to specify which metrics to calculate and and to calculate them also in the selector object. This means both our decision tree json files and our selector object are not expanding beyond just selection. In practice, the config file that we'll be specifying with the --tree option will not be more than just the tree, but I'd be hesitant to break workflows by changing the options name.

I don't have any great suggestions for better terminology, but I'll keep thinking.