This exists already, but will need updates based on more recent work prior to GA: https://docs.openshift.com/service-mesh/3.0.0tp1/update/ossm-updating-openshift-service-mesh.html

We'll need an upgrade section that covers two types of upgrades, which users may want to treat differently:

• Minor upgrades (e.g. 3.0 -> 3.1)
• Patch upgrades (e.g. 3.0.0 -> 3.0.1)

This section should also give an overview of the topics: In Place vs Revision Based upgrades, Istio Revisions, Tags, etc. as well as how the Istio and IstioRevision resources work together. These topics will be common to both of the above upgrade types.

Upstream doc:

https://github.com/istio-ecosystem/sail-operator/blob/main/docs/README.md#concepts

https://github.com/istio-ecosystem/sail-operator/blob/main/docs/README.md#update-strategy

Note: There are potential enhancements it may also describe automatic vs manual upgrades and if proxies are automatically reset (possible future features). Covered by this epic: https://issues.redhat.com/browse/OSSM-5897. This can be deferred if not complete when this story is picked up.