Add approval information and other enhancements to rbt land JSON output.

Review Request #12170 — Created March 17, 2022 and submitted — Latest diff uploaded




rbt land --json now includes information on whether the change was
approved (helping to differentiate approval failures from other
failures), as well as including information on the review request that
failed approval.

When successful, the payloads for each landed review request now always
has a type key (which will be patch when applying a review request
via an ID), and will always contain a source_branch (which defaults to
null). This creates consistency in the payload.

Tested landing approved changes.

Tested attempting to land unapproved changes.

Tested attempting to land changes and hitting (manufactured) errors.

In all cases, I saw the output I expected.