[ADD] zero_stock_approval: add "zero_stock_approval" field in SO

[stan-odoo]

Currently, Sales/Users can confirm quotations without any approval.

This change introduces a new module "zero_stock_approval" which adds:

• A boolean field "zero_stock_approval" on sales orders
• A computed field "is_manager" to identify whether the current user is a Sales/Administrator

Behavior:

• If "zero_stock_approval" is checked, Sales/Users can confirm the quotation
• If unchecked, Sales/Users cannot confirm the quotation
• The "zero_stock_approval" field is read-only for Sales/Users and can only be set by Sales/Administrators

This ensures proper approval control and restricts confirmation rights based on the approval status.

task-5081749

[robodoo]