Update Istio must-gather tag

From slack

Update this topic:
https://docs.openshift.com/container-platform/4.11/service_mesh/v2x/ossm-troubleshooting-istio.html#ossm-about-collecting-ossm-data_troubleshooting-ossm

registry.redhat.io/openshift-service-mesh/istio-must-gather-rhel8

should something like:

registry.redhat.io/openshift-service-mesh/istio-must-gather-rhel8:2.2

Additional slack discussion:

The previous latest tag is no longer in that registry for safety reasons
https://coreos.slack.com/archives/C01R9E3SFEV/p1661796103465749