Integrate relations for remote objects (#4754)

Foreign table id cannot be a foreign key of a base table. But the
current code use foreign keys to link object metadata with activities,
events... So we will:
- create a column without creating a foreign key
- add a comment on the table schema so pg_graphql sees it as a foreign
key

This PR:
- refactor a bit object metadata service so the mutation creation is
separated into an util
- adds the mutation creation for remote object relations
- add a new type of mutation to create a comment

---------

Co-authored-by: Thomas Trompette <thomast@twenty.com>

packages/twenty-server/src/engine/api/graphql/workspace-query-builder/factories/foreign-data-wrapper-query.factory.ts

@@ -25,7 +25,8 @@ export class ForeignDataWrapperQueryFactory {
     foreignDataWrapperId: string,
     userMappingOptions: UserMappingOptions,
   ) {
-    return `CREATE USER MAPPING IF NOT EXISTS FOR ${userMappingOptions.username} SERVER "${foreignDataWrapperId}" OPTIONS (user '${userMappingOptions.username}', password '${userMappingOptions.password}')`;
+    // CURRENT_USER works for now since we are using only one user. But if we switch to a user per workspace, we need to change this.
+    return `CREATE USER MAPPING IF NOT EXISTS FOR CURRENT_USER SERVER "${foreignDataWrapperId}" OPTIONS (user '${userMappingOptions.username}', password '${userMappingOptions.password}')`;
   }
 
   private buildNameAndOptionsFromType(