Adds Danger and a rule showing build size differences (#11865)

* Adds danger_js with an initial rule for warning about large PRs

Signed-off-by: Anandaroop Roy <[email protected]>

* [WIP] Get the before and after for the build results

* [Dev] More work on the Dangerfile

* [Danger] Split the reports into sections based on their package

* Remove the --extract-errors on the circle build

* [Danger] Improve the lookup for previous -> current build to also include the environment

* Fix rebase