Deprecate dataSource table with dual-write to workspace.databaseSchema (#19059)

## Summary
- Starts deprecation of the `core.dataSource` table by introducing a
dual-write system: `DataSourceService.createDataSourceMetadata` now
writes to both `core.dataSource` and `core.workspace.databaseSchema`
- Migrates read sites (`WorkspaceDataSourceService.checkSchemaExists`,
`WorkspaceSchemaFactory`, `MiddlewareService`,
`WorkspacesMigrationCommandRunner`) to read from
`workspace.databaseSchema` instead of querying the `dataSource` table
- Removes the unused `databaseUrl` field from `WorkspaceEntity` and
drops the column via migration
- Adds a 1.20 upgrade command to backfill `workspace.databaseSchema`
from `dataSource.schema` for existing workspaces

packages/twenty-front/src/testing/mock-data/users.ts

@@ -158,8 +158,7 @@ export const mockCurrentWorkspace = {
     },
   ],
   workspaceMembersCount: 1,
-  databaseSchema: '',
-  databaseUrl: '',
+  databaseSchema: null,
   isTwoFactorAuthenticationEnforced: false,
   eventLogRetentionDays: 90,
   __typename: 'Workspace',