add notification to Envoy related tabs when your dataplane is offline

[johncowen]

Description

## Why

We have this issue kumahq/kuma#5216 over in backend which has been open for quite a while. I would guess (and I could be wrong) that this generally happens when your dataplane is offline, something we know in the GUI

What

We should render one of our notifications if you visit any of these Envoy related tabs saying something like:

"your dataplane is offline so you will not get any information here, but here's the error anyway"

(obvs better wording)

We do this in the Dataplane Traffic viz already, but we should also check that we either cannot open a drawer when this happens or that (if we can) we show similar notifications.

If we do this I would imagine we can close the backend issue, unless I've totally misunderstood the original reaosn for the issue.

[johncowen]

Triage: there is another case where this can error, and that is when we are trying to get stats via several hops, i.e. via the control-plane > zone control-plane > dataplane.

Lets do two things:

1. If the dataplane is offline. Lets either gray out the tabs or show a yellow notification (my opinion is we show notification seeing as we do this elsewhere, whereas we never gray out tabs)
2. If we get an error when the dataplane is online, lets hardcode our own more human error into the error message. We believe the error message that comes from the backend isn't that useful for the user. Maybe check with @bartsmykla if we can easily change the backend message to be more human also.

If we do these two things we can close this issue and close the upstream backend issue (kumahq/kuma#5216)