Switch to keycloak from auth0

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Fixes #120

• install https://www.npmjs.com/package/eslint-plugin-react-hooks (and update other eslint plugins at the same time to make it work). Moved to a new issue Install eslint-plugin-react-hooks #124
• Hopefully fix the non-automatic rerendering after keycloak init. We'll skip this for now, moved here Render username on page load instead of Log in if the user is already logged in #123
• Fix redirect after login
• Uninstall unused deps
• Remove old unused env vars
• Turn hardcoded urls into env vars
• Clean up

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So I think I've started plugging stuff in correctly now. Now you can click Login and you won't be sent to auth0, but you're sent to e.g.

http://localhost:3000/undefined/protocol/openid-connect/auth?client_id=realities&redirect_uri=http%3A%2F%2Flocalhost%3A3000%2F3c198940-etc&state=eccd53df-etc&response_mode=fragment&response_type=code&scope=openid&nonce=51b0d8etc

which doesn't really log you in, gonna research this a bit more

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Added redirectUri option to login() but didn't seem to change anything.

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Ah the config keycloak generated for me was pretty bad, I had to have url instead of auth-server-url

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Got 502 bad gateway when trying to register a new account after clicking on login

POST https://auth.platoproject.org/auth/realms/plato/login-actions/registration?session_code=CwWzetc&execution=f1d63d95-etc&client_id=realities&tab_id=ZUYetc

Edit: the registration seems to have worked anyway, since next time i click Login I get correctly redirected back to Realities