Give readonly access to payment orders to the Accounting / Read Only group

[sbidoul]

Is your feature request related to a problem?

Currently payment orders are fully accessible to the Accounting / Payments group.

Describe the solution you'd like

Since Odoo has an Accounting / Readonly Group, it is useful to give readonly access to payment orders to this group too.

Alternatives considered

Create an Payments Read Only group, but that seems superfluous.

Additional context

This should not expose additional sensitive information that is not otherwise already accessible to a user with full readonly access to accounting.