The website customer portal has been reorganized so non-sales portal features can be used without requiring sales tools. Customer-facing discussion areas for quotes and online sales now use a shared messaging component, making portal communication more consistent and easier to maintain.

- split website_portal_sale from website_portal to remove sale dependency
- add a generic chatter template and controller to website_portal (and use it in website_quote and website_sale)

This update improves how follower updates are handled in Odoo's messaging features, making the process more reliable when applied to multiple records. It also fixes related record creation behavior for linked fields, reducing the chance of inconsistent follower or relationship data.

In particular: avoid to use the field method `convert_to_write`, and generalize
it for recordsets.