Add pyyaml for management of docker-compose yaml files

[deverickapollo]

Summary
This PR adds the python3-yaml package as a dependency in UmbrelOS. The addition of this package is necessary to manage Docker-Compose YAML files effectively within UmbrelOS.

Changes
Added python3-yaml to the list of essential system utilities installed during the OS build process.
Removed duplicate installs of python3.

Reasoning
The python3-yaml package is required for parsing and managing YAML files, which are commonly used for Docker-Compose configurations. By including this package, we ensure UmbrelOS can handle Docker-Compose YAML files out of the box, improving the overall functionality and app developer experience.

Testing
❌ Built UmbrelOS with the updated Dockerfile.
❌ Verified that python3-yaml is installed and functional.
✅ Tested Docker-Compose YAML file management to ensure compatibility and functionality.

Notes
No breaking changes are introduced with this PR. The addition of python3-yaml is backward-compatible and should not affect existing functionality.

[deverickapollo]

Hi team! Circling back to open a discussion on dynamically managing yaml files. I am currently leveraging pyyaml to manage the btcpay configuration from user preferences. The immediate use case will be to optionally support monero within BTCPayServer.