fastapi: add dev envs support

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

fastapi/compose.yaml

@@ -1,10 +1,11 @@
 services:
   api:
-    build: .
+    build:
+      context: .
+      target: builder
     container_name: fastapi-application
     environment:
       PORT: 8000
     ports:
       - '8000:8000'
     restart: "no"
-