Upversion stx-horizon image to Openstack Antelope

As part of the STX-Openstack upversion to Antelope, the stx-horizon
image is being upversioned to the Antelope (stable/2023.1) branch [1]

Due to an issue with the wheels version (launchpad #2027616) [2], we're unable to build the images with the changes of this review, because of that, the test plan for this review will not contemplate the build of the image, and testing it on an environment with STX-Openstack.

Only after this launchpad is worked on, we can proceed with the test plan, but, considering that the only possible option for the PROJECT_REF of this image is the `stable/2023.1` branch (in the context of the Antelope upversion), and that this is the only change this review is doing, it's ready for review.

It's worth noticing that these images are not being build in the official StarlingX build process, so there's no impact on the build itself.

It is possible that the customization commands on this file will require changes in the future, we will only be sure on that when the image is fully buildable and further tests applied.

[1] https://opendev.org/openstack/horizon/src/branch/stable/2023.1
[2] https://bugs.launchpad.net/starlingx/+bug/2027616

Test Plan:
PASS: Make sure the branch specified in the is used when building the image PROJECT_REF

Story: 2010715
Task: 48123

Change-Id: Ia3687f35f0e784be20a0909fcc9116cb50e18b02
Signed-off-by: Romulo Leite <romulo.leite@windriver.com>

upstream/openstack/python-horizon/debian/stx-horizon.stable_docker_image

@@ -2,7 +2,7 @@ BUILDER=loci
 LABEL=stx-horizon
 PROJECT=horizon
 PROJECT_REPO=https://opendev.org/openstack/horizon.git
-PROJECT_REF=e6f3952b878d6b04fde9742987e0f37a1cfad3e5
+PROJECT_REF=stable/2023.1
 PROJECT_UID=42425
 PROJECT_GID=42425
 PIP_PACKAGES="pycryptodomex python-ceilometerclient \