Update Dockerfile

[rizlas]

Hi,
I just updated the Dockerfile of netbox-sync image. Here's a recap:

• Update base image to debian 12
• Install dependencies via venv in order to avoid copy of useless packages in the next stage
• Do not upgrade images as base images are always upgraded and it is not a common best practice
• Removed pip install wheel as is already specified in requirements.txt
• Changed from adduser and addgroup to useradd and groupadd
• Use dockerignore instead of copy specific files
• Removed dockerfile from image. Could lead to a security flaw/issue.
• Updated urllib package to the latest minor
• Added PATH and TZ environment variables. Former is needed to use venv packages, latter to have consistent logging time.

The overall images size is now ~40MB smaller.
Other packages, in particular pyvmomi needs an update, but there might be some breaking changes to deal with.

[bb-Ricardo]

This looks great, thank you very much. I like it a lot