[embeddable] make presentation interface names consistent (#205279)

PR cleans up presentation interface names for consistentency
* adds `$` suffix to all observables. For example, `dataLoading` =>
`dataLoading$`
* removes `Panel` naming convention from interface names since an api
may not be a panel, an api may be a dashboard. For example,
`PublisesPanelTitle` => `PublishesTitle`

#### Note to Reviewers
Pay special attention to any place where your application creates an
untyped API. In the example below, there is no typescript violation when
the parent returns `dataLoading` instead of `dataLoading$` since the
parent is not typed as `PublishesDataLoading`. Please check for
instances like these.

```
<ReactEmbeddableRenderer
  getParentApi={() => {
    dataLoading: new BehaviorSubject()
  }}
/>
```

---------

Co-authored-by: Elastic Machine <elasticmachine@users.noreply.github.com>
Co-authored-by: kibanamachine <42973632+kibanamachine@users.noreply.github.com>

examples/embeddable_examples/public/app/render_examples.tsx

@@ -47,7 +47,7 @@ export const RenderExamples = () => {
   const [api, setApi] = useState<SearchApi | null>(null);
   const [hidePanelChrome, setHidePanelChrome] = useState<boolean>(false);
   const [dataLoading, timeRange] = useBatchedOptionalPublishingSubjects(
-    api?.dataLoading,
+    api?.dataLoading$,
     parentApi.timeRange$
   );