Add yaml_definition_file columns to ai_catalog_item_versions

What does this MR do and why?

Adds database columns to support storing YAML definitions in object storage:

• yaml_definition_file: path to the uploaded file
• yaml_definition_store: storage type identifier (defaults to 1)
• Check constraint for file path length (max 255 chars)

This is Part 1a of a series splitting up !227895 to add object storage support for large YAML definitions in the AI Catalog.

MR Series

MR	Description	Dependencies
1a (this MR)	Add yaml_definition_file columns to ai_catalog_... (!228120 - merged)	None
1b	Add ai_catalog object storage configuration and... (!228122 - merged)	None
2	YamlDefinitionUploader (CarrierWave uploader)	1b
3	Model layer: Mount uploader, add transparent accessor	1a, 2
4	Service layer & schema: Upload in services, make yaml_definition optional	3

Issue: #591638

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