Update Dockerfile to install poetry and tox

.devcontainer/Dockerfile

@@ -1,16 +1,21 @@
 FROM mcr.microsoft.com/vscode/devcontainers/base:ubuntu-20.04
 
+# Install all Python versions supported by EDGAR
 RUN apt-get update && apt-get install -y \
     software-properties-common \
-    && add-apt-repository ppa:deadsnakes/ppa
-
-RUN apt-get update && apt-get install -y \
+    && add-apt-repository ppa:deadsnakes/ppa \
+    && apt-get update && apt-get install -y \
     python3.9 python3.9-dev python3.9-venv \
     python3.10 python3.10-dev python3.10-venv \
     python3.11 python3.11-dev python3.11-venv \
-    python3.12 python3.12-dev python3.12-venv
+    python3.12 python3.12-dev python3.12-venv curl
+
+# This installs pip from the primary version of Python we'll use
+# for development
+RUN curl -sS https://bootstrap.pypa.io/get-pip.py | python3.12
 
-RUN update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.9 1 \
-    && update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.10 2 \
-    && update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.11 3 \
-    && update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.12 4
+# Install pipx, poetry, and tox
+RUN python3.12 -m pip install --upgrade pip \
+    && python3.12 -m pip install pipx \
+    && python3.12 -m pipx ensurepath \
+    && pipx install poetry tox

.devcontainer/devcontainer.json

@@ -17,7 +17,6 @@
             ]
         }
     },
-    "postCreateCommand": "python3 --version",
-    "forwardPorts": [],
+    "postCreateCommand": "python3 --version && poetry --version && tox --version",
     "remoteUser": "vscode"
 }