container: default FROM_IMAGE to Rocky Linux 10

Since tentacle, the preferred base image for ceph containers has been
Rocky Linux 10, and the CI tag-naming logic in build.sh already assumes
rockylinux-10 is the default fromtag for every branch except reef and
squid.  The actual build default was never flipped, though: anything
that ran build.sh without FROM_IMAGE set (e.g. the release container
job in ceph-build) still got a CentOS Stream 9 base.

Flip the Containerfile ARG and the build.sh fallback to
docker.io/rockylinux/rockylinux:10 so umbrella and later build from
Rocky 10 by default.  Builds that want a different base can still pass
FROM_IMAGE explicitly, as the CI pipeline does.

Signed-off-by: David Galloway <david.galloway@ibm.com>

container/Containerfile

@@ -1,4 +1,4 @@
-ARG FROM_IMAGE="quay.io/centos/centos:stream9"
+ARG FROM_IMAGE="docker.io/rockylinux/rockylinux:10"
 FROM $FROM_IMAGE
 
 # allow FROM_IMAGE to be visible inside this stage

container/build.sh

@@ -16,7 +16,7 @@ usage() {
 $0 [containerfile] (defaults to 'Containerfile')
 For a CI build (from ceph-ci.git, built and pushed to shaman):
 CI_CONTAINER: must be 'true'
-FROM_IMAGE: defaults to quay.io/centos/centos9:stream
+FROM_IMAGE: defaults to docker.io/rockylinux/rockylinux:10
 FLAVOR (OSD flavor, default or crimson)
 BRANCH (of Ceph. <remote>/<ref>)
 CEPH_SHA1 (of Ceph)
@@ -125,7 +125,7 @@ CONTAINER_BUILD_ARGS=(
     --squash
     -f "$CFILE"
     -t build.sh.output
-    --build-arg FROM_IMAGE="${FROM_IMAGE:-quay.io/centos/centos:stream9}"
+    --build-arg FROM_IMAGE="${FROM_IMAGE:-docker.io/rockylinux/rockylinux:10}"
     --build-arg CEPH_SHA1="${CEPH_SHA1}"
     --build-arg CEPH_GIT_REPO="${CEPH_GIT_REPO}"
     --build-arg CEPH_REF="${BRANCH:-main}"