[18.0][FIX] stock_picking_origin_reference_sale: set origin_reference from Sales Order ignoring customer reference

[Jay2163]

Description of the issue:
When a Sales Order has a Customer Reference (client_order_ref), the Delivery Order origin field includes both the SO name and the customer reference (e.g., "SO00029 - ABC123").
This prevents the Delivery Order from having a clickable link to the originating Sales Order.

Current behavior:

• Delivery Order origin = "SO00029 - ABC123" (plain text)
• No clickable link to the SO in the transfer.

Expected behavior:

• The Delivery Order should maintain a clickable link to the Sales Order via the origin_reference field.
• The origin field can still show the descriptive text including the customer reference.

Solution implemented:

• Added a convert_origin method to extract only the SO name from origin.
• Updated _compute_origin_reference to search for the SO using the extracted name and set origin_reference.
• Ensures that Delivery Orders now correctly link back to the originating Sales Order without modifying the descriptive origin.

Affected versions:

• Odoo 18.0

Example:

• origin = "SO00029 - ABC123"
• origin_reference = "sale.order,42" (clickable link to SO)

Impact

Restores expected behavior of the Delivery Orders by ensuring the Source Document link (origin_reference) correctly points to the originating Sales Order, even when a Customer Reference is present.

Fixes issue #2116