Add an empty .airflowignore file when creating a new project with astro dev init

[odaneau-astro]

• I have checked that a similar feature request does not already exist.

✍️ Is your feature request related to a problem? Please describe.
Not a problem, just a simple thought.

astro dev init already provides sample files for airflow_settings.yaml, .env and many others.

🧩 Describe the solution you'd like
We should provide dags/.airflowignore out of the box as well.

🤔 Describe alternatives you've considered
Create it manually.

Is your feature request specific to a particular Astronomer Platform?

• Astro
• Software
• None/Unknown

💡 Additional context