refactor: Make the Dockerfile a tiny bit cache friendlier

[maringuu]

Still not great as the whole installation happens after copying but at least copying is not the first thing we do anymore.

Related #124

[jstucke]

The code looks fine, the container builds without errors but when trying to use it in FACT it crashes directly:

Traceback (most recent call last):
  File "/venv/lib/python3.11/site-packages/gunicorn/arbiter.py", line 609, in spawn_worker
    worker.init_process()
  File "/venv/lib/python3.11/site-packages/gunicorn/workers/base.py", line 134, in init_process
    self.load_wsgi()
  File "/venv/lib/python3.11/site-packages/gunicorn/workers/base.py", line 146, in load_wsgi
    self.wsgi = self.app.wsgi()
                ^^^^^^^^^^^^^^^
  File "/venv/lib/python3.11/site-packages/gunicorn/app/base.py", line 67, in wsgi
    self.callable = self.load()
                    ^^^^^^^^^^^
  File "/venv/lib/python3.11/site-packages/gunicorn/app/wsgiapp.py", line 58, in load
    return self.load_wsgiapp()
           ^^^^^^^^^^^^^^^^^^^
  File "/venv/lib/python3.11/site-packages/gunicorn/app/wsgiapp.py", line 48, in load_wsgiapp
    return util.import_app(self.app_uri)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/venv/lib/python3.11/site-packages/gunicorn/util.py", line 371, in import_app
    mod = importlib.import_module(module)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/importlib/__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "<frozen importlib._bootstrap>", line 1206, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1178, in _find_and_load
  File "<frozen importlib._bootstrap>", line 1142, in _find_and_load_unlocked
ModuleNotFoundError: No module named 'server'

Maybe because server.py is not found in the cwd because the WORKDIR changed

[maringuu]

Mhh, well good catch. The underlying problem here is that the fact_extractor does not have a proper python module structure.
Lets conside the tree -L 2 of this repository.

.
├── Dockerfile
├── extract.py
├── fact_extractor # This is a namespace pacakge
│   ├── config
│   ├── docker_extraction.py
│   ├── fact_extract.py # Does not use relative imports, but resides in the same directory as the modules it imports
│   ├── helperFunctions # This is a package
│   ├── install
│   ├── install.py
│   ├── plugins
│   ├── __pycache__
│   ├── server.py # Should use relative imports
│   ├── test
│   ├── unpacker
│   └── version.py

I would expect fact_extractor to be a regular package and the files to use imports like import fact_extractor.helperFunctions.
Interestingly, this is not the case but the imports look like import helperFunctions.
Actually, the package fact_extractor is not used at all.
The reason this works is, that python adds the current working directory to the module search path.

Before this patch the dockerfile changed the workdir to the path the modules reside in.
To acoomodate this, I set the PYTHONPATH to /app.
The easy fix here is to simply change the PYTHONPATH to /app/fact_extractor (I'll do this) but I think in the future a proper module strucutre should be used.

[jstucke]

LGTM!