tsweb: change RequestID format to have a date in it

So we can locate them in logs more easily.

Updates tailscale/corp#24721

Change-Id: Ia766c75608050dde7edc99835979a6e9bb328df2
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

cmd/derper/derper_test.go

@@ -109,6 +109,7 @@ func TestDeps(t *testing.T) {
 			"gvisor.dev/gvisor/pkg/tcpip/header": "https://github.com/tailscale/tailscale/issues/9756",
 			"tailscale.com/net/packet":           "not needed in derper",
 			"github.com/gaissmai/bart":           "not needed in derper",
+			"database/sql/driver":                "not needed in derper", // previously came in via github.com/google/uuid
 		},
 	}.Check(t)
 }