Update aggregate API to use binary megabytes and enhance documentation

- Changed API responses and internal calculations to use binary megabytes (MiB) instead of octets for traffic metrics.
- Updated relevant endpoints in AGGREGATE.md to reflect the new metric units.
- Modified handler and merge logic to accommodate the new data structure and ensure accurate traffic reporting.
- Enhanced tests to validate the changes in traffic calculations and summary data.
- Deprecated the use of total_octets in favor of total_megabytes for consistency across the API.

internal/aggregate/handlers_test.go

@@ -49,7 +49,7 @@ func TestHandlerResolveAndFetch(t *testing.T) {
 	if err := json.Unmarshal(rec.Body.Bytes(), &env); err != nil {
 		t.Fatal(err)
 	}
-	if !env.OK || env.Data.FleetTotalOctets != 42 {
+	if !env.OK || env.Data.FleetTotalMegabytes != octetsToMegabytes(42) {
 		t.Fatalf("data: %+v", env.Data)
 	}
 }