[feature] Add a request ID and include it in logs (#1476)

This adds a lightweight form of tracing to GTS. Each incoming request is
assigned a Request ID which we then pass on and log in all our log
lines. Any function that gets called downstream from an HTTP handler
should now emit a requestID=value pair whenever it logs something.

Co-authored-by: kim <grufwub@gmail.com>

internal/cache/util.go

@@ -35,5 +35,5 @@ func tryUntil(msg string, count int, do func() bool) {
 			return
 		}
 	}
-	log.Panicf("failed %s after %d tries", msg, count)
+	log.Panicf(nil, "failed %s after %d tries", msg, count)
 }