feat: exclusively allow db access from backend

[eensander]

This PR:

• removes policies for RLS,
• removes the contradicting DISABLE ROW LEVEL SECURITY for the project table,
• replaces supabase client on server with supabase servicerole client (in definition and utilization),
• revokes privileges for anon and authenticated according to this discussion, omitting the service_role
• disables PostgREST's OpenAPI spec endpoint according to that same discussion

@CvdL-UM: I'm creating a PR and request your to review these changes since I have tried running the Cypress tests but am running into some errors that seem to be unrelated to my changes. Can you please verify that my changes introduce no problems?

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Name	Status	Preview	Comments	Updated (UTC)
lawnotation	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Mar 14, 2024 3:00pm

[CvdL-UM]

End-2-end testing has passed successfully. Keep in mind that not all functionalities are covered by e2e testing at the moment. I will add additional tests the coming time. Would it be a good idea to first merge @YamainReisig's changes for the authorization with matching e2e tests?