[Threat Hunting Investigations] Improve API docs for notes/timeline (#213584)

## Summary

[META
issue](https://github.com/elastic/security-docs-internal/issues/57)

This PR improves the API documentation for timeline/notes/pinned events
as per the definition in the meta issue.

### Notes
#### Timeline API
- `eventType`:
	- is always set to `all`
	- looks like it's been superseded by dataView?
	- I marked it as `deperecated` 
- `eventIdToNoteIds`:
- there's a type mismatch between what the frontend expects and what is
returned
	- also it does not seem to be used anymore?
	- it needs to be investigated further
#### Notes API
- `GlobalNote`:
	- looks like it's not used anymore
	- I removed it, nothing broke
- `eventIngested`, `eventTimestamp`, `eventDataView` and `overrideOwner`
are all not used on the patch note endpoint, I removed them. The
`event*` ones I have never seen before to be honest.

---------

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

x-pack/test/api_integration/services/security_solution_api.gen.ts

@@ -1300,7 +1300,7 @@ finalize it.
         .send(props.body as object);
     },
     /**
-     * Pin an event to an existing Timeline.
+     * Pin/unpin an event to/from an existing Timeline.
      */
     persistPinnedEventRoute(props: PersistPinnedEventRouteProps, kibanaSpace: string = 'default') {
       return supertest