[ecovacs] Allow loading device descriptions from a user file (#14873)

[ecovacs] Allow loading device descriptions from a user file (#14873)

* [ecovacs] Allow loading device descriptions from a user file

If a new device is released within our release cycle, getting the
description for that device into the binding was impossible for users
before. With this change, they can create an override file in their
installation (with contents we'll need to supply to them), which serves
as a stop-gap solution until the next OH release.

Signed-off-by: Danny Baumann <dannybaumann@web.de>