Test configuration reloading on Kubernetes

[binarylogic]

This might already be done, but it's part of our "Plan Of Attack" in #2222. The purpose is to ensure that config reloading works properly:

• Reloading works as expected when a new valid config is provided.
• Vector does not exit when a new invalid config is provided.
• Vector logs a warning when a new invalid config is provided, but it should not replace the config. It should continue with the old config until a valid config is provided.
• Vector eventually recovers when a new valid config is provided.

It's likely all of these are satisfied but I want to add explicit tests for these. See #2002.

If any of these tests fail we should open issues for the work.

[MOZGIII]

Since we went with explicit config reloading at #2222, I'm closing this as no longer relevant.

Vector won't reload config on the fly, and instead we'll rely on kubectl rollout restart -n vector ds/vector to update the config.