IntersectionObserver API not accepting specific element

### Description

As we can see [here in the proposed API](https://github.com/w3c/IntersectionObserver/blob/main/explainer.md#proposed-api), the `IntersectionObsserver` accepts options when created and accept a specific element to observe when we want to begin observe (which also decoupled from the initialization of the observer, but in the AMP observer API we cant specify which element we want to observe. i would like to be able to specify which element I want to observer because in my Ad component i have a "feed
" which allows for many ads to be shown and i want to be able to track them separately

### Alternatives Considered

Maybe my request can be solved with the current available features but i couldnt find any data in the README,, if so i would appreciate if someone could point me to the relevant documentation.

### Additional Context

_No response_

Start by reviewing the proposed IntersectionObserver API and the current AMP observer API, including the README mentioned in the issue. Determine how an individual element could be selected for observation and whether existing documentation already covers this. Done means the requested per-element observation behavior is supported or the relevant limitation is clearly documented.

Written by the indexing model from the issue text.