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/webhook/standard-objects/webhook.workspace-entity.ts

@@ -2,12 +2,13 @@ import { FieldMetadataType } from 'src/engine/metadata-modules/field-metadata/fi
 import { BaseWorkspaceEntity } from 'src/engine/twenty-orm/base.workspace-entity';
 import { WorkspaceEntity } from 'src/engine/twenty-orm/decorators/workspace-entity.decorator';
 import { WorkspaceField } from 'src/engine/twenty-orm/decorators/workspace-field.decorator';
+import { WorkspaceIsDeprecated } from 'src/engine/twenty-orm/decorators/workspace-is-deprecated.decorator';
 import { WorkspaceIsNotAuditLogged } from 'src/engine/twenty-orm/decorators/workspace-is-not-audit-logged.decorator';
 import { WorkspaceIsNullable } from 'src/engine/twenty-orm/decorators/workspace-is-nullable.decorator';
 import { WorkspaceIsSystem } from 'src/engine/twenty-orm/decorators/workspace-is-system.decorator';
 import { WEBHOOK_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 { WorkspaceIsDeprecated } from 'src/engine/twenty-orm/decorators/workspace-is-deprecated.decorator';
 
 @WorkspaceEntity({
   standardId: STANDARD_OBJECT_IDS.webhook,
@@ -15,7 +16,7 @@ import { WorkspaceIsDeprecated } from 'src/engine/twenty-orm/decorators/workspac
   labelSingular: 'Webhook',
   labelPlural: 'Webhooks',
   description: 'A webhook',
-  icon: 'IconRobot',
+  icon: STANDARD_OBJECT_ICONS.webhook,
   labelIdentifierStandardId: WEBHOOK_STANDARD_FIELD_IDS.targetUrl,
 })
 @WorkspaceIsNotAuditLogged()