use Poetry to deal with deps and package install

As the new-age Python package manager, Poetry brings a lot
of good additions to the table. It allows us to more easily
deal with virtualenvs for the project and resolve dependencies.

As of this commit, `requirements.txt` is replaced by Poetry,
configured at `pyproject.toml`.

In Docker and GitLab, we currently use Poetry in a root fashion.
We should work toward purely using virtualenvs in Docker, but,
for now we'd like to move forward with other things. The project
can still be installed to a virtualenv and used on a user's system
through Poetry; it is just not yet doing so in Docker.

Modifications:

* docker/scripts/install-deps.sh
    * Remove python dependencies.
* conf/config.defaults
    * Script paths have been updated to use '/usr/bin'.
* docker/git-entrypoint.sh
    * Use '/usr/bin/aurweb-git-auth' instead of
      '/usr/local/bin/aurweb-git-auth'.

Additions:

* docker/scripts/install-python-deps.sh
    * A script used purely to install Python dependencies with Poetry.
      This has to be used within the aurweb project directory and
      requires system-wide dependencies are installed beforehand.
    * Also upgrades system-wide pip.

Signed-off-by: Kevin Morris <kevr@0cost.org>

Dockerfile

@@ -1,23 +1,25 @@
 FROM archlinux:base-devel
 
+ENV PATH="$HOME/.poetry/bin:${PATH}"
 ENV PYTHONPATH=/aurweb
 ENV AUR_CONFIG=conf/config
 
+# Install system-wide dependencies.
+COPY ./docker/scripts/install-deps.sh /install-deps.sh
+RUN /install-deps.sh
+
 # Copy Docker scripts
 COPY ./docker /docker
 COPY ./docker/scripts/*.sh /usr/local/bin/
 
-# Install system-wide dependencies.
-RUN /docker/scripts/install-deps.sh
-
 # Copy over all aurweb files.
 COPY . /aurweb
 
 # Working directory is aurweb root @ /aurweb.
 WORKDIR /aurweb
 
-# Install pip directories now that we have access to /aurweb.
-RUN pip install -r requirements.txt
+# Install Python dependencies.
+RUN /docker/scripts/install-python-deps.sh
 
 # Add our aur user.
 RUN useradd -U -d /aurweb -c 'AUR User' aur
@@ -27,6 +29,3 @@ RUN ln -sf /usr/share/zoneinfo/UTC /etc/localtime
 
 # Install translations.
 RUN make -C po all install
-
-# Install package and scripts.
-RUN python setup.py install --install-scripts=/usr/local/bin