Update Dockerfile to Multi-Stage

[multi-stager]

Overview

Hi,

Thanks for maintaining pygeoapi. I represent a research group investigating multi-stage builds. We recently refactored your Dockerfile to a multi-stage Dockerfile and found that it brings the following benefits:

✅ Reduced final image size (from 1236MB to 101MB)
✅ Minimized image vulnerabilities (verified via Trivy, from 890 to 47)

We hope this small improvement to the Dockerfile will be useful to you :)

Thanks,

Related Issue / discussion

None

Additional information

Dependency policy (RFC2)

• I have ensured that this PR meets RFC2 requirements

Updates to public demo

• I have ensured that breaking changes to the pygeoapi master demo server have been addressed
  • https://github.com/geopython/demo.pygeoapi.io/blob/master/services/pygeoapi_master/local.config.yml

Contributions and licensing

(as per https://github.com/geopython/pygeoapi/blob/master/CONTRIBUTING.md#contributions-and-licensing)

• I'd like to contribute [feature X|bugfix Y|docs|something else] to pygeoapi. I confirm that my contributions to pygeoapi will be compatible with the pygeoapi license guidelines at the time of contribution
• I have already previously agreed to the pygeoapi Contributions and Licensing Guidelines

[justb4]

This kind of contribution is very welcome as the Docker Image needs slimming. And multi-staged is one of the ways to go.
But...unfortunately it is not as easy as just copying the /pygeoapi directory in the target image. If you look at the Dockerfile you will see that a whole list of Debian and Python packages are installed, plus additional resources. Those are also required in the final Docker Image.

[multi-stager]

@justb4 You're right — our current multi-stage approach misses critical dependencies. We'll refine the split to properly slim the image while preserving functionality. Appreciate the feedback!

[tomkralidis]

Closing. echo @justb4's comments. Suggest discussing in #1753 to gain clarity and consensus as a first step.