Read useBackendPlugin from jsonData

[brojd]

Read useBackendPlugin from jsonData. Passing meta to window object is done to avoid unnecessary changes in http interceptors and requests. This hack will be removed once we enable backend plugin by default - it's just for development purposes

Checklist

• [ ] Unit, integration, and e2e (if applicable) tests updated
• [x] Documentation added (or pr:no public docs PR label added if not required)
• [x] Added the relevant release notes label (see labels prefixed w/ release:). These labels dictate how your PR will show up in the autogenerated release notes.