Add CORS support and response caching to aggregate endpoints

- Introduced CORS configuration options in config.example.yaml, allowing specification of allowed origins for cross-origin requests.
- Enhanced the aggregate handler to support response caching with a configurable TTL, improving performance for repeated requests.
- Updated the aggregate API to return a structured response indicating whether any upstream requests failed, enhancing error handling and response clarity.
- Modified documentation in AGGREGATE.md and README.md to reflect the new CORS and caching features.
- Added tests to validate the new functionality in the aggregate handler.

internal/aggregate/merge_test.go

@@ -119,6 +119,55 @@ func TestBuildSummary(t *testing.T) {
 	}
 }
 
+func TestBuildUsersMergeLimits(t *testing.T) {
+	tag1 := "aa"
+	tag2 := "bb"
+	expLater := "2030-01-02T00:00:00Z"
+	expEarlier := "2020-01-02T00:00:00Z"
+	m20 := uint64(20)
+	m10 := uint64(10)
+	q500 := uint64(500)
+	q100 := uint64(100)
+	results := []ServerFetchResult{
+		{
+			Alias: "b", OK: true,
+			Users: []UserInfo{{
+				Username: "u", TotalOctets: 1, CurrentConnections: 0,
+				UserAdTag: &tag2, MaxTCPConns: &m20, ExpirationRFC3339: &expLater,
+				DataQuotaBytes: &q500, MaxUniqueIPs: &m10,
+			}},
+		},
+		{
+			Alias: "a", OK: true,
+			Users: []UserInfo{{
+				Username: "u", TotalOctets: 1, CurrentConnections: 0,
+				UserAdTag: &tag1, MaxTCPConns: &m10, ExpirationRFC3339: &expEarlier,
+				DataQuotaBytes: &q100, MaxUniqueIPs: &m20,
+			}},
+		},
+	}
+	rows := BuildUsers(results, false, 0)
+	if len(rows) != 1 {
+		t.Fatalf("rows: %+v", rows)
+	}
+	r := rows[0]
+	if r.UserAdTag == nil || *r.UserAdTag != tag1 {
+		t.Fatalf("ad tag want first alias order a: got %v", r.UserAdTag)
+	}
+	if r.MaxTCPConns == nil || *r.MaxTCPConns != 10 {
+		t.Fatalf("max tcp want min 10: %v", r.MaxTCPConns)
+	}
+	if r.ExpirationRFC3339 == nil || *r.ExpirationRFC3339 != expEarlier {
+		t.Fatalf("expiration want earliest: %v", r.ExpirationRFC3339)
+	}
+	if r.DataQuotaBytes == nil || *r.DataQuotaBytes != 100 {
+		t.Fatalf("quota want min: %v", r.DataQuotaBytes)
+	}
+	if r.MaxUniqueIPs == nil || *r.MaxUniqueIPs != 10 {
+		t.Fatalf("max unique ips want min: %v", r.MaxUniqueIPs)
+	}
+}
+
 func TestBuildUsersMinOctets(t *testing.T) {
 	results := []ServerFetchResult{
 		{Alias: "a", OK: true, Users: []UserInfo{{Username: "low", TotalOctets: 5}}},