Add FK creation in migration v2 (#14685)

## Context
-
packages/twenty-server/src/engine/metadata-modules/object-metadata/utils/build-default-relation-flat-field-metadatas-for-custom-object.util.ts
Fixing targetFlatFieldMetadata not being accurate for default relation
during object creation (was not used yet)
-
packages/twenty-server/src/engine/twenty-orm/workspace-schema-manager/services/workspace-schema-foreign-key-manager.service.ts
Simplifying API + Removing unused methods and the ones that were
querying pg schema as we want to avoid those as much as possible
-
packages/twenty-server/src/engine/workspace-manager/workspace-migration-v2/workspace-migration-runner-v2/action-handlers/field/services/create-field-action-handler.service.ts
Adding FK creation when Join column is created

packages/twenty-server/src/engine/metadata-modules/object-metadata/utils/build-default-relation-flat-field-metadatas-for-custom-object.util.ts

@@ -239,7 +239,7 @@ export const buildDefaultRelationFlatFieldMetadatasForCustomObject = ({
             },
             flatRelationTargetObjectMetadata:
               fromFlatObjectMetadataToFlatObjectMetadataWithoutFields(
-                sourceFlatObjectMetadata,
+                targetFlatObjectMetadata,
               ),
           },
         ],
@@ -254,7 +254,7 @@ export const buildDefaultRelationFlatFieldMetadatasForCustomObject = ({
             },
             flatRelationTargetObjectMetadata:
               fromFlatObjectMetadataToFlatObjectMetadataWithoutFields(
-                targetFlatObjectMetadata,
+                sourceFlatObjectMetadata,
               ),
           },
         ],