Create example DAGs for the currently supported checks

[tatiana]

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Context

At the moment the Astro Python SDK exposes three types of checks:

• AggregateCheck
• BooleanCheck
• StatsCheck

However, we have not written significant documentation about them.

Acceptance Criteria

• [ ] One or multiple example(s) DAG illustrating these use cases
• [ ] Enable these new example DAGs to run as part of our CI checks