Remove releasever from manifests; add pungi treefile stubs

As agreed in https://gitlab.com/fedora/bootc/tracker/-/issues/39, we're
going to be maintaining the treefile for all Fedora versions in the
`main` branch. Accordingly stop hardcoding releasevers and repos in
the treefiles.

But for now, we're still building the official image in pungi using the
non-container-native path, so add compatibility stubs to not break it.

Coincidentally, this doubles down on the proposed API to build the base
images for different Fedora versions using the `--from` switch. Document
this in the README. But note this doesn't work yet because nothing is
telling rpm-ostree which repos to use or what the releasever should be.

README.md

@@ -32,6 +32,18 @@ podman build --security-opt=label=disable --cap-add=all \
 
 See the `Containerfile` for more details. This builds the default `tier-1` image.
 
+## Fedora versions
+
+By default, the base images are built for Fedora rawhide. To build against a
+different Fedora version, you can override the `FROM` image used to obtain the
+Fedora repos and dnf variables. E.g.:
+
+```
+podman build --from quay.io/fedora/fedora:41 ...
+```
+
+WIP: THIS DOESN'T WORK YET.
+
 ### Deriving
 
 You are of course also free to fork, customize, and build base images yourself.

fedora-40.yaml

@@ -0,0 +1,7 @@
+# NB: This treefile is used by the legacy pungi path only to build tier-1. It
+# will be removed in the future.
+releasever: 40
+repos:
+  - fedora
+  - fedora-updates
+include: fedora-bootc.yaml

fedora-41.yaml

@@ -0,0 +1,7 @@
+# NB: This treefile is used by the legacy pungi path only to build tier-1. It
+# will be removed in the future.
+releasever: 41
+repos:
+  - fedora
+  - fedora-updates
+include: fedora-bootc.yaml

fedora-bootc.yaml

@@ -1,7 +1,3 @@
-releasever: rawhide
-repos:
-  - rawhide
-
 metadata:
   name: fedora-boot-tier1
   summary: Fedora Bootable Tier 1

fedora-rawhide.yaml

@@ -0,0 +1,6 @@
+# NB: This treefile is used by the legacy pungi path only to build tier-1. It
+# will be removed in the future.
+releasever: rawhide
+repos:
+  - fedora-rawhide
+include: fedora-bootc.yaml

fedora-tier-0.yaml

@@ -1,7 +1,3 @@
-releasever: rawhide
-repos:
-  - rawhide
-
 metadata:
   name: fedora-boot-tier0
   summary: Fedora Bootable Tier 0

fedora-tier-x.yaml

@@ -1,7 +1,3 @@
-releasever: rawhide
-repos:
-  - rawhide
-
 metadata:
   name: fedora-boot-tier-x
   summary: Fedora Bootable Tier X