lib/pull: Add collection support to ostree_repo_pull_with_options()
This adds a new collection-refs option of type a(sss), giving a list of
(collection ID, ref name, checksum) tuples to pull from the given remote.
This option is intended to supersede the refs and override-commit-ids
options, so is mutually exclusive with them.
This includes support for resolving the refs from the remote’s summary
file, or from its refs/heads and refs/mirrors directories.
Signed-off-by: Philip Withnall <withnall@endlessm.com>
Closes: #924
Approved by: cgwalters