Add frontend hubspot tracker

... but we probably want it to be on the back end. Oh, well.

frontend/src/hooks/useHubSpotTracker.ts

@@ -0,0 +1,25 @@
+type FlagEnabledEvent = {
+    email: string;
+    client_id: string;
+    date: Date;
+    project: string;
+    environment_type: string;
+};
+
+type SdkConnectedEvent = {
+    client_id: string;
+    date: Date;
+    // the same thing we report via the unleash-sdk header, e.g. unleash-client-js:1.0.0
+    sdk: string;
+    app_name: string;
+};
+
+type HubSpotEvent = FlagEnabledEvent | SdkConnectedEvent;
+
+export const useHubSpotTracker = () => {
+    const trackEvent = (event: HubSpotEvent) => {
+        // todo: implement
+    };
+
+    return { trackEvent };
+};