Update .devcontainer configurations

.devcontainer/Dockerfile

@@ -0,0 +1,24 @@
+# Use the Ubtuntu base image
+FROM ubuntu:22.04
+
+# Download development tools
+RUN apt-get update
+RUN apt-get install -y curl
+RUN apt-get install -y git
+RUN apt-get install -y unzip
+
+# Run the container as a user
+RUN useradd -m -s /bin/bash slackdev
+RUN chown slackdev /usr/local/bin
+USER slackdev
+
+# Install the project runtime
+RUN curl -fsSL https://deno.land/install.sh | sh
+RUN export DENO_INSTALL="/home/slackdev/.deno"
+RUN export PATH="$DENO_INSTALL/bin:$PATH"
+
+# Set the working directory
+WORKDIR /workspaces
+
+# Install the Slack CLI
+RUN curl -fsSL https://downloads.slack-edge.com/slack-cli/install.sh | bash -s -- -d

.devcontainer/README.md

@@ -0,0 +1,35 @@
+# .devcontainer
+
+A [development container][container] provides a predefined environment with
+some tools needed for development, which can be useful in editors such as
+[Visual Studio Code][vscode] or remote settings like [Codespaces][codespaces].
+
+This specific container packages [the Slack CLI][cli] with the project runtime
+and a few development tools. The `Dockerfile` details the container.
+
+## Editor extensions
+
+Modifications to an editor can be made with changes to the `devcontainer.json`
+file:
+
+```diff
+{
+    "customizations": {
+        "vscode": {
+            "extensions": [
++               "GitHub.copilot",
+                "denoland.vscode-deno",
+                "ms-azuretools.vscode-docker"
+            ],
++           "settings": {
++               "terminal.integrated.defaultProfile.linux": "zsh"
++           }
+        }
+    }
+}
+```
+
+[codespaces]: https://github.com/features/codespaces
+[cli]: https://api.slack.com/automation/cli
+[container]: https://containers.dev/
+[vscode]: https://code.visualstudio.com/docs/devcontainers/containers

.devcontainer/devcontainer.json

@@ -0,0 +1,13 @@
+{
+    "name": "Slack Platform",
+    "dockerFile": "Dockerfile",
+    "remoteUser": "slackdev",
+    "customizations": {
+        "vscode": {
+            "extensions": [
+                "denoland.vscode-deno",
+                "ms-azuretools.vscode-docker"
+            ]
+        }
+    }
+}