This commit adds a key called DeployCollectionID to the flatpakref and
flatpakrepo file formats, which is intended to replace the CollectionID
key (which is still supported but deprecated). The reason for the change
is the same as for the metadata key change from xa.collection-id to
ostree.deploy-collection-id, which is that old versions of Flatpak
(roughly 0.9.8 through 1.0.1 depending on compile time options) hit
various bugs when collection IDs are in use. Flathub will soon enable
the metadata key to deploy collection IDs, and this change means Flathub
can also deploy the collection ID in flatpakref and flatpakrepo files
without affecting old clients.
Adding DeployCollectionID to the flatpakref and flatpakrepo files will
mean the flathub remote can be automatically configured with a
collection ID without depending on the metadata key to do that.
Closes: #2329
Approved by: alexlarsson
Not being documented makes it hard to know that this actually
takes the url of a flatpakrepo file, as opposed to the other url
key in this file, which takes the url to a remote.
