[Request]: Document alert data for observability rule types

### Description

### 🍒 Summary

We save different alert information for different observability rule types. This information can be used in multiple features such as [maintenance window](https://www.elastic.co/guide/en/kibana/current/maintenance-windows.html) and conditional actions:

We would like to document the alert data available in all the observability rules and the differences between rules so that our users can get an idea of how to filter their alerts for the above-mentioned features.

### Resources

Here is a [list of fields ](https://docs.google.com/spreadsheets/d/1tVPzZn6RTDfdyHrlsTBSyZbkm_H6szWLG7KI8n-2QHo/edit?usp=sharing)that I am preparing based on fields that we define in code such as [default_alert_as_data](https://github.com/elastic/kibana/blob/main/src/platform/packages/shared/kbn-rule-data-utils/src/default_alerts_as_data.ts).

### Which documentation set does this change impact?

Stateful and Serverless

### Feature differences

No difference

### What release is this request related to?

N/A

### Collaboration model

The documentation team

### Point of contact.

**Main contact:** @maryam-saeidi

**Stakeholders:** @jasonrhodes, @drewpost