Initial packaging draft

See #1.

The following details are implemented:

• packages: python3-streamtrain-api and streamtrain-api
• systemd.service is configured
• nginx snippet is provided
• separate user is created

The following details are missing:

• fastapi_utils needs to be replaced
  • my initial attempt with apscheduler failed, since it only recently implemented a good fastapi integration (in v4.0; this is not packaged for Debian, yet)
  • Thus, another alternative scheduler (or a manually created task) need to be integrated/implemented.
• testing whether the package actually works

The packaging is done in the last two commits. The others are just preparations.