Produce and submit a PR upstream to Nextcloud and CERNBox, such that they can validate their compliance to the OCM spec

[mickenordin]

[MahdiBaghbani]

For Nextcloud:

• Add OCM Test Suite matrix workflow for Nextcloud nextcloud/server#57274

For CERNBox:

• Add OCM Test Suite matrix workflow for CERNBox reva#5458