Example storyline overview in Airflow core docs

### Description

As described in https://cwiki.apache.org/confluence/display/AIRFLOW/Examples+Refurbish

New examples are made including tutorials. This should be weaved into the general Airflow docs in the howto section thus people can see, find and learn from the examples

### Use case/motivation

Airflow Examples have been grown in number and focus over the past years. They purpose multiple things:

Serve as tutorials to learn Airflow DAG implementation
Serve with code snippets for documentation
Serve for testing the setup
(some) service for CI integration testing

Some example DAGs are in a good quality, some are not following best practices. Current examples do not follow a structure.

There are example DAGs contained in the Airflow core (currently pushed to standard provider/example_dags) as well as there are more examples in other providers. But examples from other providers are lot loaded automatically.

So in the [Airflow 3 Dev Calls](https://cwiki.apache.org/confluence/display/AIRFLOW/Airflow+3+Dev+call%3A+Meeting+Notes#Airflow3Devcall:MeetingNotes-22May2025) there was a demand named to clean-up and optimize example DAGs.

### Related issues

_No response_

### Are you willing to submit a PR?

- [ ] Yes I am willing to submit a PR!

### Code of Conduct

- [x] I agree to follow this project's [Code of Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)

Start by reviewing the Examples Refurbish proposal and the general Airflow documentation's howto section, then inspect the standard provider/example_dags and the references to examples from other providers. Done means the relevant example DAGs are discoverable in a coherent storyline that helps readers learn Airflow DAG implementation.

Written by the indexing model from the issue text.