create org.osbuild.ostree.aleph stage

Similar to the aleph file created for builds of FCOS based on ostree
commit inputs, this adds an aleph file that contains information about
the initial deployment of data when the disk image was built

A new stage is preferred here as both the org.osbuild.ostree.deploy
and org.osbuild.ostree.deploy.container stages need an aleph file and
use of the aleph file may depend on the project/product. For example,
right now CoreOS is the only project that uses an aleph file, but others
may want it in the future.

osbuild/util/ostree.py

@@ -228,6 +228,34 @@ def deployment_path(root: PathLike, osname: str, ref: str, serial: int):
     return sysroot
 
 
+def parse_origin(origin: PathLike):
+    """Parse the origin file and return the deployment type and imgref
+
+    Example container case: container-image-reference=ostree-remote-image:fedora:docker://quay.io/fedora/fedora-coreos:stable
+    Example ostree commit case: refspec=fedora:fedora/x86_64/coreos/stable
+    """
+    deploy_type = ""
+    imgref = ""
+    with open(origin, "r", encoding="utf8") as f:
+        for line in f:
+            separated_line = line.split("=")
+            if separated_line[0] == "container-image-reference":
+                deploy_type = "container"
+                imgref = separated_line[1].rstrip()
+                break
+            if separated_line[0] == "refspec":
+                deploy_type = "ostree_commit"
+                imgref = separated_line[1].rstrip()
+                break
+
+    if deploy_type == "":
+        raise ValueError("Could not find 'container-image-reference' or 'refspec' in origin file")
+    if imgref == "":
+        raise ValueError("Could not find imgref in origin file")
+
+    return deploy_type, imgref
+
+
 class PasswdLike:
     """Representation of a file with structure like /etc/passwd