Use ASL 2.0

Use LICENSE.txt, dco, and contributing files in your repositories. See examples below.

https://github.com/quarkusio/quarkus/blob/main/LICENSE.txt 

https://github.com/quarkusio/quarkus/blob/main/dco.txt 

https://github.com/quarkusio/quarkus/blob/main/CONTRIBUTING.md

You do not need to and should not reference the license in every single file of the repository (assuming you have done the steps above), see example below:

https://github.com/quarkusio/quarkus/blob/main/core/runtime/src/main/java/io/quarkus/runtime/Application.java  (no header)

https://raw.githubusercontent.com/quarkusio/quarkus/main/docs/src/main/asciidoc/continuous-testing.adoc  (no header in doc)