search: capitalize operators in human query strings
Created by: rvantonder
Stacked on https://github.com/sourcegraph/sourcegraph/pull/36761.
As in title, cosmetic change. It's more obvious that operators like AND
have special meaning when capitalized in alerts as introduced in https://github.com/sourcegraph/sourcegraph/pull/36761, because we don't highlighting those queries.
Test plan
Updated tests.