Enhance API routing and testing for user endpoints

- Updated the reverse proxy to redirect `GET` requests for `/api/{alias}/users` to `/v1/stats/users`, ensuring compatibility with Telemt builds that handle these requests differently.
- Added tests to verify that `GET` and `HEAD` requests to `/api/{alias}/users` are correctly rewritten, while `POST` requests and user-specific retrievals remain unchanged.
- Improved documentation in GATEWAY_RUN.md to clarify the behavior of the API routing and the importance of using the correct base URL.

internal/proxy/reverse_test.go

@@ -75,6 +75,81 @@ func TestDirectorRewritesPathWithAPIBasePath(t *testing.T) {
 	assertSameURL(t, cap.got.URL, want)
 }
 
+func TestDirectorGETUsersListUsesStatsUsers(t *testing.T) {
+	target, err := url.Parse("http://127.0.0.1:9")
+	if err != nil {
+		t.Fatal(err)
+	}
+	cap := &captureTransport{}
+	rp := NewReverseProxy(target, "/api/mtg", "/v1", "")
+	rp.Transport = cap
+
+	req, err := http.NewRequestWithContext(context.Background(), http.MethodGet, "http://127.0.0.1:9/api/mtg/users", nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	rp.ServeHTTP(httptest.NewRecorder(), req)
+
+	if cap.got == nil {
+		t.Fatal("no outgoing request captured")
+	}
+	want, err := url.Parse("http://127.0.0.1:9/v1/stats/users")
+	if err != nil {
+		t.Fatal(err)
+	}
+	assertSameURL(t, cap.got.URL, want)
+}
+
+func TestDirectorPOSTUsersCreateNotRewritten(t *testing.T) {
+	target, err := url.Parse("http://127.0.0.1:9")
+	if err != nil {
+		t.Fatal(err)
+	}
+	cap := &captureTransport{}
+	rp := NewReverseProxy(target, "/api/mtg", "/v1", "")
+	rp.Transport = cap
+
+	req, err := http.NewRequestWithContext(context.Background(), http.MethodPost, "http://127.0.0.1:9/api/mtg/users", nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	rp.ServeHTTP(httptest.NewRecorder(), req)
+
+	if cap.got == nil {
+		t.Fatal("no outgoing request captured")
+	}
+	want, err := url.Parse("http://127.0.0.1:9/v1/users")
+	if err != nil {
+		t.Fatal(err)
+	}
+	assertSameURL(t, cap.got.URL, want)
+}
+
+func TestDirectorGETUsersByNameNotRewritten(t *testing.T) {
+	target, err := url.Parse("http://127.0.0.1:9")
+	if err != nil {
+		t.Fatal(err)
+	}
+	cap := &captureTransport{}
+	rp := NewReverseProxy(target, "/api/mtg", "/v1", "")
+	rp.Transport = cap
+
+	req, err := http.NewRequestWithContext(context.Background(), http.MethodGet, "http://127.0.0.1:9/api/mtg/users/alice", nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	rp.ServeHTTP(httptest.NewRecorder(), req)
+
+	if cap.got == nil {
+		t.Fatal("no outgoing request captured")
+	}
+	want, err := url.Parse("http://127.0.0.1:9/v1/users/alice")
+	if err != nil {
+		t.Fatal(err)
+	}
+	assertSameURL(t, cap.got.URL, want)
+}
+
 func TestDirectorRewritesNestedStatsUsers(t *testing.T) {
 	target, err := url.Parse("http://127.0.0.1:9/api/")
 	if err != nil {