Refactor object metadata service (#8123)

## Context
ObjectMetadataService became quite large and handles too many
responsibilities. I'm trying to refactor a bit this part in preparation
of a larger work that will combine object-metadata services and
sync-metadata logic

- Created a STANDARD_OBJECT_ICONS that can be reused in relation
creation to refer to a standard object icon.
- Created a STANDARD_OBJECT_FIELD_IDS that can be used with an object
name to get its standard field ids.
- Moved migration, record and relation creations to dedicated services,
refactored to improve performances and readability
- Refactored some validation logic

---------

Co-authored-by: Charles Bochet <charles@twenty.com>

packages/twenty-server/src/modules/attachment/standard-objects/attachment.workspace-entity.ts

@@ -13,6 +13,7 @@ import { WorkspaceIsSystem } from 'src/engine/twenty-orm/decorators/workspace-is
 import { WorkspaceJoinColumn } from 'src/engine/twenty-orm/decorators/workspace-join-column.decorator';
 import { WorkspaceRelation } from 'src/engine/twenty-orm/decorators/workspace-relation.decorator';
 import { ATTACHMENT_STANDARD_FIELD_IDS } from 'src/engine/workspace-manager/workspace-sync-metadata/constants/standard-field-ids';
+import { STANDARD_OBJECT_ICONS } from 'src/engine/workspace-manager/workspace-sync-metadata/constants/standard-object-icons';
 import { STANDARD_OBJECT_IDS } from 'src/engine/workspace-manager/workspace-sync-metadata/constants/standard-object-ids';
 import { ActivityWorkspaceEntity } from 'src/modules/activity/standard-objects/activity.workspace-entity';
 import { CompanyWorkspaceEntity } from 'src/modules/company/standard-objects/company.workspace-entity';
@@ -28,7 +29,7 @@ import { WorkspaceMemberWorkspaceEntity } from 'src/modules/workspace-member/sta
   labelSingular: 'Attachment',
   labelPlural: 'Attachments',
   description: 'An attachment',
-  icon: 'IconFileImport',
+  icon: STANDARD_OBJECT_ICONS.attachment,
   labelIdentifierStandardId: ATTACHMENT_STANDARD_FIELD_IDS.name,
 })
 @WorkspaceIsSystem()