[16.0][ADD] sale_partner_sale_contact[_on_project]: Add sale contact to orders, invoices and projects

[maisim]

New modules: Sale Contact Management

This PR introduces two complementary modules for managing sale contacts across the sales workflow:

sale_partner_sale_contact

• Adds a sale_contact_partner_id field to sales orders and invoices
• Allows selecting a specific contact person from the customer's organization
• Automatically propagates the contact from order to invoice
• Optional display on PDF reports (configurable in settings)
• Auto-switches customer to parent company when a contact person is selected

sale_partner_sale_contact_on_project

• Extends the contact management to projects
• Automatically copies the sale contact when creating projects from sales orders
• Maintains contact information throughout the project lifecycle

Use case

In B2B scenarios, you often deal with specific contacts within a customer organization (procurement managers, project leads, etc.). While the invoice must go to the company, you need to track who you're actually working with for follow-ups, communication, and relationship management.

Design choices

• Uses child contact hierarchy (existing Odoo pattern)
• Auto-switch behavior prevents accidental invoicing to individuals while preserving contact info
• Optional restriction modules available via settings for stricter enforcement
• No modification of core partner/invoice logic - purely additive

Benefits

• Better contact tracking across sales → invoice → project workflow
• Cleaner reports with relevant contact information
• Improve global consistncy and avoid to get stuffs like Analytic Account linked to a person
• Respects commercial entity relationships while maintaining operational contacts
• All features are backward compatible and don't affect existing workflows. 🤞

Related PRs

You can optionally use this module to limit partner_id selection to companies

• account_invoice_partner_id_company_only: Restrict partner to companies [16.0][ADD] account_invoice_partner_id_company_only: Restrict partner… account-invoicing#2180
• project_partner_id_company_only: Restrict partner to company [16.0][ADD] project_partner_id_company_only: Restrict partner to company project#1611
• sale_partner_id_company_only: Restrict partner to companies [16.0][ADD] sale_partner_id_company_only: Restrict partner to companies #4042