Documentation enhancement: mention amp-story-auto-analytics from amp-analytics dev docs page

### Description

I was trying to get `` to work with web stories. There was this blog (https://blog.amp.dev/2019/08/28/analytics-for-your-amp-stories/), but it did not say where to put the element (and it was not working for me). E.g. should it go in `` or `` or `` etc. Eventually I stumbled across `` - I suggest mentioning this on the `` documentation page as the amp-analytics page is included in the "stories" drop down as being relevant for web stories.

(Could also improve the documentation for amp-analytics to explain how to use the element in a web story. I could not find an example.)

### Alternatives Considered

I looked at some blog posts etc, but stumbled upon amp-story-auto-analytics just because I was looking down the side bar.

### Additional Context

_No response_

Open the amp-analytics developer documentation page and review its Web Stories guidance alongside the amp-story-auto-analytics component and the linked AMP blog post. Update the documentation to explain which element to use and where it belongs in a Web Story, with an example if the existing docs support one. Done means the page clearly directs Web Stories users to amp-story-auto-analytics.

Written by the indexing model from the issue text.