Support budgets

[stevehipwell]

Following the announcement of enterprise scoped budgets adding support for both enterprise and organization budgets would be useful.

[gmlewis]

This would be a great PR for any new contributor to this repo or a new Go developer.
All contributions are greatly appreciated!

Feel free to volunteer for any issue and the issue can be assigned to you so that others don't attempt to duplicate the work.
Also feel free to perform a code review on any PR that has the label "NeedsReview" - we appreciate those contributions too!
We have a REVIEWERS file that you could add your username to if you are willing to be contacted when reviews are needed.

Please check out our CONTRIBUTING.md guide to get started. (In particular, please remember to go generate ./... and don't use force-push to your PRs.)

Thank you!

[youneedgreg]

Kindly assign this to me.

[gmlewis]

Kindly assign this to me.

Thank you, @youneedgreg! It's yours.