Make predictor top-level key, update documentation and examples

[vishalbollu]

closes #

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checklist:

• run make test and make lint
• test end to end manually (i.e. build/push all images, restart operator, and run cortex deploy --refresh)
• update the examples
• update the docs and add any new files to summary.md
• merge to master
• cherry-pick into release branches if applicable
• check that the docs are up-to-date in gitbook
• alert the dev team if the dev environment changed
• delete the branch once it's merged