Migrate user_permission_export_upload_uploads to gitlab_main_user

Summary

Updates the database dictionary for user_permission_export_upload_uploads table to reflect its migration from gitlab_main to gitlab_main_user schema.

What does this MR do?

• Updates db/docs/user_permission_export_upload_uploads.yml to specify the new schema location
• Aligns the table configuration with our sharding guidelines
• Updates the sharding issue

Why are we making this change?

The gitlab_main schema is being deprecated as part of our database sharding initiative. All tables currently residing in gitlab_main need to be migrated to their appropriate target schemas. Setting this table to the same schema gitlab_main_user as the parent table user_permission_export_uploads. This table can later be sharded using uploaded_by_user_id (effectively user_id).

Schema Migration Details

• Table: user_permission_export_upload_uploads
• From: gitlab_main
• To: gitlab_main_user
• Feature Category: permissions

Review Request

@krasio

Related Links

• Database Sharding Guidelines
• [Schema Migration Tracking Issue] (#556057)
• [Schema Selection Guidelines] (https://docs.gitlab.com/development/cells/#available-cells--organization-schemas)
• This table is the partition to store the uploads (metadata) for the parent table user_permission_export_uploads