Missing API for changing secret of a dbus collection

Nobody has claimed this yet.

Unlike `portal::Keyring`, we currently have no (direct) way to change the password of a `dbus::Collection`. I think the main problem here is that changing a collection password isn't part of the secret-service dbus specification.

Seahorse / gnome keyring work around this and have something custom implemented (`org.gnome.keyring.InternalUnsupportedGuiltRiddenInterface`).

A possible workaround I can see at the moment would be to load the collection as a keyring file via `portal::Keyring` and change the password there - although I'm not sure how many side effects it would have to fiddle with the keyring file directly instead of using the intended oo7/secret-service api.

I wonder if this is something we can fix on oo7 side, or if we need an updated/extended secret-service dbus specification.

Start by comparing the existing portal::Keyring password-changing API with dbus::Collection and reviewing the secret-service D-Bus specification. Examine the Seahorse/GNOME keyring workaround and determine whether oo7 can expose a safe API or whether the specification needs an extension; done means a decided, documented path for changing collection passwords.

Written by the indexing model from the issue text.