Remove foreign key constraints from work_item_type_id columns

MRs:

• Remove foreign key constraints from work_item_t... (!221910 - merged)
• Remove FK from work_item_type_user_preferences (!222551 - merged)

Description

As part of implementing configurable work item types with Option 4 (single column approach), we need to remove foreign key constraints from work_item_type_id columns.

This is necessary because we'll be storing both positive IDs (system-defined types) and negative IDs (custom types) in the same column, which breaks traditional foreign key relationships.

Proposal

Problem: The existing foreign key constraints from work_item_type_id to work_item_types table prevent us from storing negative IDs for custom work item types.

Solution: Create a database migration that drops the foreign key constraints from work_item_type_id columns in these tables:

• issues
• work_item_type_custom_fields
• work_item_type_custom_lifecycles
• work_item_custom_status_mappings
• work_item_type_user_preferences (this one requires investigation)