Centralize metadata relations constant + simplification (#16901)

# Introduction
As we introduced a new grain on relation extraction thanks to low level
`SyncableEntity` and `WorkspaceRelatedEntity` we're able to strictly
typesafe extract metadata entity

The new constant centralizes both many to one and one to many constants
metadata entity constants in a more strictly typesafe way. Remains only
the flatEntityForeignKey aggregator which has to be chosen manually
across all available targeted flat entity ids properties

packages/twenty-server/src/engine/metadata-modules/route-trigger/services/workspace-flat-route-trigger-map-cache.service.ts

@@ -6,9 +6,9 @@ import { Repository } from 'typeorm';
 
 import { WorkspaceCacheProvider } from 'src/engine/workspace-cache/interfaces/workspace-cache-provider.service';
 
-import { ALL_METADATA_RELATION_PROPERTIES } from 'src/engine/metadata-modules/flat-entity/constant/all-metadata-relations-properties.constant';
 import { createEmptyFlatEntityMaps } from 'src/engine/metadata-modules/flat-entity/constant/create-empty-flat-entity-maps.constant';
 import { FlatEntityMaps } from 'src/engine/metadata-modules/flat-entity/types/flat-entity-maps.type';
+import { getMetadataEntityRelationProperties } from 'src/engine/metadata-modules/flat-entity/utils/get-metadata-entity-relation-properties.util';
 import { RouteTriggerEntity } from 'src/engine/metadata-modules/route-trigger/route-trigger.entity';
 import { FlatRouteTrigger } from 'src/engine/metadata-modules/route-trigger/types/flat-route-trigger.type';
 import { WorkspaceCache } from 'src/engine/workspace-cache/decorators/workspace-cache.decorator';
@@ -40,9 +40,7 @@ export class WorkspaceFlatRouteTriggerMapCacheService extends WorkspaceCacheProv
     for (const routeTriggerEntity of routeTriggers) {
       const routeTriggerEntityWithoutRelations = removePropertiesFromRecord(
         routeTriggerEntity,
-        Object.keys(
-          ALL_METADATA_RELATION_PROPERTIES.routeTrigger,
-        ) as (keyof typeof ALL_METADATA_RELATION_PROPERTIES.routeTrigger)[],
+        getMetadataEntityRelationProperties('routeTrigger'),
       );
       const flatRouteTrigger = {
         ...routeTriggerEntityWithoutRelations,