Add step to add a rotation timer job

When a new release is branched, we need to ensure that a proper rotation
job is set for the respective release. In this example, we instantiate a
new timer for rotation of the images

Signed-off-by: Ritesh Raj Sarraf <ritesh.sarraf@collabora.com>

content/guides/apertis_release_process.md

@@ -127,6 +127,7 @@ Host images.apertis.org
   * Restart the OBS schedulers
 * Update build suffix on OBS Project configuration (eg. `bv2019.0b<B_CNT>`, `bv2020dev0b<B_CNT>`). Please refer to section **Build Suffix** for more details about it
 * Add a directory for the release to the LAVA NFS path at: `/srv/images/public/lava/nfs/` on host images.apertis.org. The LAVA test jobs pick the kernel and initrd image from the release's directory path. Refer to the README for details
+* Instantiate a *new timer to rotate images* for the new release (eg. On host `aura`, run command `systemctl enable --now rotate-images@v2019.timer`)
 * Update the [ci-package-builder](https://gitlab.apertis.org/infrastructure/ci-package-builder/) to target the next release
 * Update the [gitlab-rulez](https://gitlab.apertis.org/infrastructure/gitlab-rulez/) recipe to point to the new development release
   * Set the default development branch for all git projects