[16.0][IMP] cooperator: Add specific income account for share increase

[nicolasramossomit]

This PR adds the capability to use a different income account for share increase operations in the cooperator module. Key changes:

1. Added new company-dependent fields:

   • property_account_income_increase_id on product.template
   • property_account_income_increase_categ_id on product.category

2. Modified invoice line preparation to use specific account for increase operations:

   • Uses new increase account when subscription type is 'increase'
   • Falls back to standard income account if increase account is not set

3. Added corresponding tests:

   • Test for standard income account in new subscriptions
   • Test for increase income account in increase subscriptions

The change allows cooperatives to track income from share increases separately from initial share subscriptions, improving financial reporting and accounting flexibility.

Technical details:

• Extends existing account fields pattern
• Maintains backward compatibility
• Fully tested with both scenarios