Suggest disabling the feature flag when stopping a no-code web experiment

[danielbachhuber]

When stopping a no-code web experiment, it's not obvious that you need to also disable the feature flag in order for your no-code changes to stop being applied.

We should either suggest that the feature flag be disabled, or disable it for them (and communicate what's happening).

I imagine the same behavior happens when running a product experiment, so we'll want to think that through too.

From https://posthoghelp.zendesk.com/agent/tickets/21962