Apply Python naming convention to the example DAGs

[BasPH]

Description

I suggest applying Python's file naming conventions to the example DAGs. Python never uses hyphens, instead uses underscores to name everything. This PR renames the example DAG filenames.

🎟 Issue(s)

Related #XXX

🧪 Functional Testing

Tested by running go build and astro dev init.

📸 Screenshots

Add screenshots to illustrate the validity of these changes.

📋 Checklist

• [ ] Rebased from the main (or release if patching) branch (before testing)
• [ ] Ran make test before taking out of draft
• [ ] Ran make lint before taking out of draft
• [ ] Added/updated applicable tests
• [ ] Tested against Astro-API (if necessary).
• [ ] Tested against Houston-API and Astronomer (if necessary).
• [ ] Communicated to/tagged owners of respective clients potentially impacted by these changes.
• [ ] Updated any related documentation