feat: extend consent management api

Introduces 2 new API endpoints to proxygui to be used by Perun for consent management by user:

• GET /users/me/consents endpoint for listing all user's consents in proxy db
• DELETE /users/me/consents/<consent_id> endpoint for deleting a specific consent

closes PRX-286

requested review from @433364

assigned to @485456

OIDC (authorization code flow and logout) should be replaced with OAuth bearer token authentication (no logout)

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• 9f0fc1ff - feat: extend consent management api

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• 977185d3 - feat: extend consent management api

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• 498df41e - feat: extend consent management api

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• d98df784 - refactor: use authlib for oauth operations

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• 1e3548f6 - refactor: use authlib for oauth operations

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requested review from @469484