disable e2e tests on most branches
Created by: nicksnyder
e2e tests and infrastructure are currently flaky enough it is not helpful to have them cause red builds.
This PR makes two changes:
- e2e tests no longer block green builds on master (they still run async).
- e2e tests no longer run on non-master branches (except for release branches and renovate branches).
See RFC 137 for more information on why we are doing this.