Feat/disable flexible backend (#1673)

* wip: refacto and start creating custom resolver

* feat: findMany & findUnique of a custom entity

* feat: wip pagination

* feat: initial metadata migration

* feat: universal findAll with pagination

* fix: clean small stuff in pagination

* fix: test

* fix: miss file

* feat: rename custom into universal

* feat: enable/disable flexible backend from env

---------

Co-authored-by: Charles Bochet <charles@twenty.com>
Co-authored-by: Charles Bochet <charlesBochet@users.noreply.github.com>

server/src/integrations/environment/environment.validation.ts

@@ -46,6 +46,11 @@ export class EnvironmentVariables {
   @IsBoolean()
   TELEMETRY_ANONYMIZATION_ENABLED?: boolean;
 
+  @CastToBoolean()
+  @IsOptional()
+  @IsBoolean()
+  FLEXIBLE_BACKEND_ENABLED?: boolean;
+
   @CastToPositiveNumber()
   @IsNumber()
   @IsOptional()