docs: Update docs to be version agnostic

Signed-off-by: Oliver Gondža <[email protected]>

Author: olivergondza

README.md

@@ -5,7 +5,7 @@
 ## Usage
 
 ```sh
-oc adm must-gather --image=registry.redhat.io/openshift-gitops-1/gitops-must-gather-rhel-8:v1.9.0
+oc adm must-gather --image=registry.redhat.io/openshift-gitops-1/gitops-must-gather-rhel-8:$GITOPS_VERSION
 ```
 
 The command above will create a local directory with a dump of the OpenShift GitOps state. Note that this command will only get data related to the GitOps Operator in your OpenShift cluster.