DOCSP-42620 -- Update default base image to ubi9 (mongodb#1858)

* DOCSP-42620 -- update default redhat base image to ubi9

* DOCSP-42620 -- external review revisions

Author: jvincent-mongodb

source/reference/helm-operator-settings.txt

@@ -228,12 +228,12 @@ The suffix of the :term:`application database` image.
 
 .. include:: /includes/summary-1-20-suffix-change.rst
 
-The default is ``ubi8``. We recommend using only ``ubi`` images for consistency, but if you need to, you can change this setting to ``ubuntu2204``.
+The default is ``ubi9``. We recommend using only ``ubi`` images for consistency, but if you need to, you can change this setting to ``ubuntu2204``.
 
 .. code-block:: yaml
 
    mongodb:
-      imageType: ubi8
+      imageType: ubi9
 
 
 multiCluster.clusterClientTimeout

source/reference/kubectl-operator-settings.txt

@@ -505,7 +505,7 @@ The suffix of the :term:`application database` image.
 
 .. include:: /includes/summary-1-20-suffix-change.rst
 
-The default is ``-ubi8``.
+The default is ``-ubi9``.
 
 .. code-block:: yaml
    :linenos:
@@ -520,7 +520,7 @@ The default is ``-ubi8``.
              imagePullPolicy: <policyChoice>
              env:
                - name: MDB_IMAGE_TYPE
-                 value: ubi8
+                 value: ubi9
 
 .. _mdb-agent-file-logging:
 

source/tutorial/plan-k8s-op-container-images.txt

@@ -21,8 +21,10 @@ Container Images
 
 When you install the |k8s-op-short|, it pulls the images from the Quay.io
 container registry. The |k8s-op-short| images are based on the
-`Red Hat UBI 8 <https://www.redhat.com/en/topics/containers>`__
-operating system. MongoDB rebuilds |k8s-op-short| images daily for the
+`Red Hat UBI 9 <https://www.redhat.com/en/topics/containers>`__
+operating system, unless you are running MongoDB 6.0.3 or lower, 
+in which case the base image is `Red Hat UBI 8 <https://www.redhat.com/en/topics/containers>`__. 
+MongoDB rebuilds |k8s-op-short| images daily for the
 latest operating system and supporting library updates.
 
 Official images provide the following advantages:
@@ -173,6 +175,9 @@ If you enable static containers:
   {+mdbagent+} container based on the |onprem| version 
   you select to manage a specific deployment. 
 
+- You must run MongoDB version 6.0.4 or greater when your |k8s-op-short| version 
+  is 1.28.0 or greater due to base image compatibility changes in the |k8s-op-short|.
+
 - With |cloud|, your {+mdbagent+} version could fall behind compatibility with the latest 
   version of |cloud| because the {+k8s-op-short+} can't call the ``agentVersion`` endpoint 
   in |cloud|. To ensure your {+mdbagent+} is up to date with |cloud|, you can perform one