Docker: Sync main Dockerfile to docker/ubuntu/Dockerfile (OSGeo#3205)

- Copies over the Ubuntu Dockerfile edited in OSGeo#3170 to the main Dockerfile in the root of the repo.
- Adds a note at the top for future edits to the file (in both files).

Additionally, this includes a temporary fix for pytest-pylint where new version finds more issues than the old one, so we need to use the old one before we fix the issues.

.github/workflows/python-code-quality.yml

@@ -113,7 +113,8 @@ jobs:
 
       - name: Run Pylint on other files using pytest
         run: |
-          pip install pytest pytest-pylint
+          pip install pytest pytest-pylint==0.19
+          echo "::warning file=.github/workflows/python-code-quality.yml,line=116,col=42,endColumn=48::Temporarily downgraded pytest-pylint to allow merging other PRs. The errors reported with a newer version seem legitimite and should be fixed (2023-10-18, see https://github.com/OSGeo/grass/pull/3205)"
           export PYTHONPATH=`grass --config python_path`:$PYTHONPATH
           export LD_LIBRARY_PATH=$HOME/install/grass84/lib:$LD_LIBRARY_PATH
           pytest --pylint -m pylint --pylint-rcfile=.pylintrc --pylint-jobs=$(nproc) \