Allow previewing of changesets for unsupported code hosts
Created by: sqs
Right now, if you try to create a patch on a repo that is not supported (eg because it's on GitLab or another non-supported code host), it is silently discarded:
This is surprising and prevents someone from trying out campaigns if their code host is not yet supported.
Proposed behavior: You can create patches on any repository (that you can view). In the list of patches, a patch that is against an unsupported repository will not have a publish button and instead will have an indication that it can't be published because the code host is not yet supported. If you try to publish them via the GraphQL API, the publish operation will fail with an error (as it does currently).
TODO(sqs): make a mock for this