Headlamp attempts to connect to every available Kubernetes context on startup

[lindblombr]

I've observed (at least in 0.25.1, where the auth exec issue has been addressed for my use case) that upon startup, Headlamp attempts to connect to every single configured Kubernetes context to retrieve cluster metadata. I believe this is not a good idea. If a user has a sizable context configuration and perhaps 2FA enabled for each context, this can cause prompts for 2FA for every configured context on startup. It should be possible to disable this behavior and, in fact, it should likely be disabled by default. Headlamp should not try to connect to any cluster unless the user specifically wants it to.

[joaquimrocha]

Dup for #2165 .