Issue #12751: Direct contributors to Bugzilla for issue tracking

[csadilek]

@gabrielluong As discussed, this will prevent new issues from being filed in this repo and point contributors to Bugzilla. This can but doesn't have to be merged right away, but once we have critical mass in moving issues over we should land this.

Similar to https://github.com/csadilek/monorepo/issues/new/choose.

(ui test, and perf. issues, we can file under the corresponding component/feature in the future.) Fixes #12751