docs: Add a guide for adjusting airflow scheduler resources

[chrishronek]

Summary

This should help your Airflow users understand how to update scheduler resources for Airflow hosted on plural.sh

Test Plan

I'm running the provided configuration in my plural.sh Airflow and it's working great 👍

Checklist

• No images hosted from dockerhub
• Are dashboards present to understand the health of the application. There must be at least 1 of these
  • all databases should have dashboards
  • ideally also have at least cpu/mem utilization dashboards for webserver tier of the app
  • you can use plural from-grafana to convert a grafana dashboard found via google to our CRD
• Are scaling runbooks present
  • all databases must have scaling runbooks
  • you can use the charts in pluralsh/module-library to accelerate this
• do you need to add config overlays?
  • inputing secrets
  • configuring autoscaling
• If there’s a web-facing component to the app, we need to support OIDC authentication and setting up private networks if no authentication option is viable
• All major clouds must be supported
  • Azure
  • AWS
  • GCP

---

A lot of the checklist items may not really apply since it's a simple doc, but let me know if there's anything else I can add 🍻

[michaeljguarino]

thanks for the contribution!