schemas ingested via repositoryFactory do not appear in the playground schemas tab

Describe the bug When implementing a custom repositoryFactory (e.g. my s3 implementation), files ingested by cubejs do not appear under the schemas tab in the playground, although measures and dimensions appear as expected.

To Reproduce Steps to reproduce the behavior:

1. Implement a custom repositoryFactory in cube.js
2. visit /#/schema in the playground
3. note that files are not listed there

Expected behavior A list of files (e.g. files ingested via s3) appears in the list

Version: v0.28.57