Apply the changes for CRW 2.15.1 (not CRW 2.15.0) + apply changes on CRW 2.15.1 related release notes.

Because of CRW-2729, we need to update the various CRW docs to no longer mention OpenJ9.

This affects the Z & P sections, where we call out different containers being installed (eg., `plugin-java11-openj9-rhel8` will be replaced with `plugin-java11-rhel8`, the same container used by x86_64 installations.).

Anywhere in the docs where we mention openJ9 as a performance improvement over openJDK should be removed.

Affected docs:

• Admin Guide 11.1. Defining the list of images to pull
• Install Guide 3.4.2.1. Preparing an private registry
• Install Guide 5.3.3. Preparing an private registry

In future, we MIGHT want to add a section on how to optionally install openJ9 instead of openJDK in the plugin-java8 and plugin-java11 containers, but that process has not been explored and it won't be a persistent fix – users would likely have to `yum install -y openj9...` every time they start the workspace and its associated sidecar container, or else would have to build their own custom sidecar container for reusability/persistence.