Add is active to overridable entities and deactivation logic for page layouts (#19200)

- Replace soft-deletion (deletedAt) with isActive boolean for
overridable entities (tabs, widgets, viewFieldGroups, viewFields).
Standard entities are deactivated (isActive: false) when removed from
update payloads, while custom entities are hard-deleted.
- When a viewFieldGroup is deactivated/deleted, its viewFields are
reassigned to the next section by position (or null if none remain).
- Add isActive: true filters to viewFieldGroup and viewField API queries
so deactivated entities are excluded from responses.

Next: 
- fields-widget-upsert.service.ts should be refactored a bit
- Add restore logic

packages/twenty-server/src/database/commands/upgrade-version-command/1-21/1-21-backfill-page-layouts-and-fields-widget-view-fields.command.ts

@@ -782,6 +782,7 @@ export class BackfillPageLayoutsAndFieldsWidgetViewFieldsCommand extends ActiveO
           },
           objectMetadataId: object.id,
           objectMetadataUniversalIdentifier: object.universalIdentifier,
+          isActive: true,
           createdAt: now,
           updatedAt: now,
           deletedAt: null,