Document instructions for upgrading a deployment without modifying any configured values

[bitjson]

Helm's --reuse-values/--reset-values flags can be very confusing to new users.

As it stands, users might assume --reuse-values will perform the expected upgrade, but because the image hash for each component is included in values.yaml, the --reuse-values flag will ensure the old images are used (though the deployment notes will seem to indicate that all components were upgraded).

Generally, the --reset-then-reuse-values PR for Helm would solve this issue if it were merged. For now, this workaround would also upgrade the deployment while re-applying previous customizations.

We should settle on a recommended strategy, then include upgrade instructions in the documentation and release notes for new versions.