Panorama-openedx-backend

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* Manage nonexistent user access configuration

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* Show "available to students" field in the "dashboard type"'s admin list.

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* Increase timeout to 60 secs in api calls

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* Add user role (dashboard_function) to the signed requests to the api.
This allows for Author, AI and Student views in SaaS modes.

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* Fix SigV4 calls

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* Return "STUDENT" user role in SAAS and CUSTOM modes.
* Return PANORAMA_DEFAULT_USER_ARN if there is no user access configuration.