Remove uvloop from default install and warn about stream+shell_command (#25929)

* Add warning about uvloop and shell_command

* Remove uvloop from docker files"

* Add ffmpeg

virtualization/Docker/Dockerfile.dev

@@ -28,7 +28,7 @@ RUN virtualization/Docker/setup_docker_prereqs
 COPY requirements_all.txt requirements_all.txt
 
 RUN pip3 install --no-cache-dir -r requirements_all.txt && \
-    pip3 install --no-cache-dir mysqlclient psycopg2 uvloop==0.12.2 cchardet cython
+    pip3 install --no-cache-dir mysqlclient psycopg2 cchardet cython
 
 # BEGIN: Development additions