Graphql commit field should include diffStats

For an MR it is possible to get diffStats that includes a listing of paths changed by the MR:

https://docs.gitlab.com/ee/api/graphql/reference/#mergerequestdiffstats https://docs.gitlab.com/ee/api/graphql/reference/#diffstats

It would be helpful to include a diffStats field in the commits field so we can see the paths affected by a given commit. This is possible with the REST API but of course that is much slower as each commit must be looked up one at at time.

We use the REST per-commit changed files lists in a webhook to be able to flag specific commits that touch certain areas of code in a project. Right now we can't do that with graphql so we are stuck doing one-by-one lookups with REST instead of a single graphql query.