continue to display redis-based usage statistics for continuity

Created by: dadlerj

After a recent conversation with a customer (https://sourcegraph.slack.com/archives/CMB6K7SMN/p1581876749102400) it struck me that we could face some risk if we switch over our backend usage stats without a more gentle transition.

Additionally, since beginning to log events internally, at least one customer has disabled that logging (due to perf fears), and at least one user has asked about an option to limit data collected.

Thankfully in https://sourcegraph.com/github.com/sourcegraph/sourcegraph/-/commit/727dcb2f6ad74f67294c4c07930e172eb2493c02 I left the redis-based stats intact, but deprecated.

This change simply swaps out what gets shown to site admins. The new data will still be what's included in pings.

Going forward, I will need to do some thinking about how to make this transition happen.

(Also, I took this opportunity to make the new usagestats search counts consistent with the old ones, by replacing SearchSubmitted with SearchResultsQueried, as is used in usagestatsdeprecated: https://sourcegraph.com/github.com/sourcegraph/sourcegraph@f00a22fa1b4e570fbd4495487fbfb92651b46af9/-/blob/web/src/tracking/services/serverAdminWrapper.tsx#L33)