Allow empty codeIntelUsage and searchUsage fields in pings

Created by: dadlerj

Looks like the ping handler is error-ing out in production for some subset of pings — e.g., screenshot from our stackdriver logs

I can't seem to find the actual error message in the logs though... Just an oddly formatted stack trace (?). It seems to fail on line 366 in handler.go: https://sourcegraph.com/github.com/sourcegraph/sourcegraph@9c3ecdcf2978261b8390e17b174da0ce6a0dc2f0/-/blob/cmd/frontend/internal/app/pkg/updatecheck/handler.go#L366

Which makes me think that perhaps codeIntelUsage is null here.

This is a bit of a shot in the dark — curious if you have other suggestions for how to inspect logs more produtively.