Update existing documentation:

• openshift-docs/modules/velero-obtaining-by-downloading.adoc

Update doc improvement:

• backup_and_restore/application_backup_and_restore/installing/oadp-installing-operator#velero-product-version

By default, OADP will install the forked versions of Velero that exist under the openshift organization. These images have minor tweaks to support the OpenShift specific use cases of using Velero with OCP. The openshift images tend to lag behind Velero upstream releases as we are more cautious about supporting older versions. Here is the default mapping of versions:
OADP Version Velero Version
v0.2.6 v1.6.0
v0.5.5 v1.7.1
v1.0.0 - v1.0.z v1.7.1
v1.1.0 v1.9.1
v1.1.1 v1.9.4
v1.1.2 v1.9.5
v1.1.3 v1.9.5
v1.2.0 v1.11.0