Switch to hardened Docker images in Dockerfiles

### Description

Following the fresh new [statement](https://www.docker.com/blog/docker-hardened-images-for-every-developer/) from Docker, hardened container images are now free and open source - which **might** mean that we could eventually utilize it in Airflow to enhance security.

The main challenge is that it requires authentication, which could be problematic legally & practically for local builds. If we get to overcome this one, implementation will be a great security improvement.

### Use case/motivation

Improve container's security

### Related issues

_No response_

### Are you willing to submit a PR?

- [x] Yes I am willing to submit a PR!

### Code of Conduct

- [x] I agree to follow this project's [Code of Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)