repo: Add ostree_repo_import_archive_to_mtree

repo: Add ostree_repo_import_archive_to_mtree

This is a more flexible version of the previous
ostree_repo_write_archive_to_mtree() which took a file reference.
This has an extensible options structure, and in particular
now supports `ignore_unsupported_content`.

I plan to use this for importing Docker images which contain device
nodes.  (There's no reason for container images to have those, so
we'll just ignore them).

Also here, just like the export variant, the caller is responsible for
setting up libarchive.