This update removes the 'Pay on Invoice' payment provider option from invoices. This change simplifies the payment process and aligns with best practices, as offering 'Pay on Invoice' for standard invoices was deemed unnecessary. It’s a minor adjustment to improve clarity and usability.

Paying an invoice with the pay-later provider "Pay on Invoice" doesn't make sense. 
Removing it from the list of available providers in such documents.

This update refines the way payment lines are handled within the restaurant POS module. The change replaces older, snake_case naming conventions with modern camelCase, ensuring better compatibility and future development. This improves the underlying payment processing system.

In this commit:
- Use the new method names in the payment adjustment flow.
- Replace deprecated snake_case methods with their camelCase equivalents for payment lines, payment terminals, and order totals.

Task:6049128

Forward-Port-Of: odoo/odoo#271792

This update refines the way payment lines are handled within the restaurant POS module. The team has switched to a more modern, camelCase naming convention for payment methods, enhancing the system's internal structure and aligning with current development standards. This change ensures smoother and more efficient payment processing.

In this commit:
- Use the new method names in the payment adjustment flow.
- Replace deprecated snake_case methods with their camelCase equivalents for payment lines, payment terminals, and order totals.

Task:6049128

Forward-Port-Of: odoo/odoo#271792

This update simplifies the way payment lines are handled within the restaurant POS module. The team has switched to a more modern naming convention (camelCase) for payment methods, improving code clarity and maintainability. This change ensures the system continues to function smoothly and efficiently.

In this commit:
- Use the new method names in the payment adjustment flow.
- Replace deprecated snake_case methods with their camelCase equivalents for payment lines, payment terminals, and order totals.

Task:6049128

This update removes an unnecessary and always-true check within the Odoo POS self-ordering module. The previous code was designed to verify if the self-ordering mode was 'qr_code', but this option is no longer valid. This change streamlines the code and improves efficiency without impacting functionality.

Description of the issue/feature this PR addresses:

Removed obsolete code checking "this.config.self_ordering_mode !== 'qr_code'". 
Since "qr_code" is not a valid value of the "self_ordering_mode" selection field.
The condition is always true.