chore: added analytics readme (#2436) (#2442)

* chore: added analytics readme (#2436)

* docs: updated readme-analytics.md (#2436)

src/utils/dp-gtm/readme-analytics.md

@@ -0,0 +1,13 @@
+## HCA Portal Analytics Config
+
+The HCA Portal reports various events using Google Analytics 4 tags. Most of these events are defined in [findable-ui](https://github.com/databiosphere/findable-ui), and are documented in its [analytics readme](https://github.com/DataBiosphere/findable-ui/blob/main/src/common/analytics/readme-analytics.md). Custom events and ids that are defined in this repo specifically are below.
+
+#### Custom Events
+
+There are no custom events configured in this repository.
+
+#### IDs used for tracking
+
+| Component                                     | Id name                            | "All Elements" or "Just Links"?   | Purpose                                       |
+| --------------------------------------------- | ---------------------------------- | --------------------------------- | --------------------------------------------- |
+| -`SectionHero`, in the "Explore Data" button- | -`button-explore-data`------------ | -"All Elements"------------------ | -To track submitted support requests--------- |