Add SQL OpenIddict login regression coverage

[Soumilgit]

Summary

• Adds shared EF OpenIddict persistence regression coverage that is generated for Postgres, MySQL, and SQL Server.
• Verifies authorization/token rows without an application reference can be saved across SQL providers, covering the issue Cannot login after setup when using Postgres DB (v7.22+) #1316 login path after initial admin setup.

Testing

• dotnet build backend/tests/Squidex.Data.Tests/Squidex.Data.Tests.csproj --no-restore --verbosity:minimal
• Full Testcontainers execution not run locally: Docker/Testcontainers cannot connect to npipe://./pipe/docker_engine on this machine.

Closes #1316

[Soumilgit]

Hi @SebastianStehle,
Please review this PR.

[SebastianStehle]

Please do not write tests for individual providers, they should work for all databases.

[SebastianStehle]

Please do not write tests for individual providers, they should work for all databases.

[Soumilgit]

Please do not write tests for individual providers, they should work for all databases.

Updated, thanks @SebastianStehle . I moved the regression coverage out of the Postgres-specific migration test and into a shared EF OpenIddict test so the generator runs it for Postgres, MySQL, and SQL Server.