fastapi: add dev envs support

Signed-off-by: Milas Bowman <milas.bowman@docker.com>

fastapi/Dockerfile

@@ -1,11 +1,26 @@
-FROM tiangolo/uvicorn-gunicorn-fastapi:python3.9-slim
+# syntax = docker/dockerfile:1.4
+
+FROM tiangolo/uvicorn-gunicorn-fastapi:python3.9-slim AS builder
 
 WORKDIR /app
 
-RUN apt update
-
 COPY requirements.txt ./
-RUN pip install --no-cache-dir -r requirements.txt
+RUN --mount=type=cache,target=/root/.cache/pip \
+    pip install -r requirements.txt
 
 COPY ./app ./app
 
+FROM builder as dev-envs
+
+RUN <<EOF
+apt-get update
+apt-get install -y --no-install-recommends git
+EOF
+
+RUN <<EOF
+useradd -s /bin/bash -m vscode
+groupadd docker
+usermod -aG docker vscode
+EOF
+# install Docker tools (cli, buildx, compose)
+COPY --from=gloursdocker/docker / /