Jeff Kinnison

[Draft] Add backend schema object

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Currently, `backend` config is recorded in a dict, inconsistent with the rest of the schema. Motivated by #3126, this adds a backend config object.

Updates: - Requirements in the "Data Sharing Requirement" document addressed - Client-side sharing utilities now load user lists via AJAX to reduce loading time - Routes added to ExperimentController and...

Updating to Pandas 2.0 resulted in a few minor errors, and this PR should handle the issues I encountered. Fixes include - `pandas.io.json.json_normalize` is now located in `pandas.json_normalize` - `pandas.set_option('display.max_colwidth',...