Frontend: Support custom YAML tag `!reference` when working with the CI schema on WebIDE

Summary

The WebIDE is now using our local CI schema (!104649 (merged)), but it is missing support for the !reference keyword since it is a custom YAML tag.

Unresolved tag: !referenceYAML(0)

Proposal

Make sure to include custom tags when registering the schema to the WebIDE. See !87826 (merged) for how it's done for the Pipeline Editor.