Downgrade dockerfile to 3.8.6 to avoid image bloat

Dockerfile

@@ -1,4 +1,4 @@
-FROM python:3.9.1-slim-buster as base
+FROM python:3.8.6-slim-buster as base
 
 # Setup env
 ENV LANG C.UTF-8

docker-compose.yml

@@ -9,7 +9,7 @@ services:
     # Build step - only needed when additional dependencies are needed
     # build:
     #   context: .
-    #   dockerfile: "./Dockerfile.technical"
+    #   dockerfile: "./docker/Dockerfile.technical"
     restart: unless-stopped
     container_name: freqtrade
     volumes: