Support user authentication via OpenID Connect

Fixes #436 (closed), see that issue for context and implementation plan.

See also https://gitlab.com/exosphere/oidc-redirector, the Flask app needed to make this work end-to-end.

How to Test

• If you haven't done so already, ask @j.michael.lowe to map your TACC username to XSEDE username on IU cloud, so that you can do an OpenID Connect federated login
• Visit https://try-dev.exosphere.app in a new browser environment (e.g. private window)
• Click "Add XSEDE account"
• You should be redirected to the Globus login page. Enter your XSEDE credentials
• After a moment, you should be redirected back to Exosphere, asked to choose projects to log into on IU cloud
• Choose at least one project, it should be added to the Exosphere UI successfully.

Screenshots