Add database constraints for Mattermost Slash Commands fields
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## Summary
##### Description:
Add database-level constraints to Mattermost Slash Commands integration fields to match the existing model validations and ensure data integrity.
##### Implementation Details:
- Add length constraints to the `chat_names` table.
- Need to investigate the appropriate length limits - these should align with what's currently enforced in the ChatName model validations
- This provides an additional layer of data validation at the database level
Acceptance Criteria:
- Create migration to add length constraints to the specified columns
- Ensure constraints align with model validation limits
- Test that the constraints work as expected for new and existing records
issue