When shutting down Edge, we should persist metrics upstream.

[chriswk]

Describe the feature request

I would like Edge to persist metrics upstream on shutdown.

Background

Currently, if Edge has persistence configured, we do already persist tokens/features to the configured persistence when shutting down. We should also make one last attempt to upload metrics to upstream when shutting down.

Solution suggestions

No response

[ivarconr]

Yes, flushing cached metrics would be preferred on shutdown. This is in line with how node SDK (and thus the proxy) do it today.

[sighphyre]

Closed by #564