Change dev environment setup to use postgresql

- sqlite causes too many errors
- fix requirements file
- fixes for docker setup
- A lot of concurrency issues
- Bite the bullet, time to go!

docker/docker-compose.dev.yml

@@ -1,8 +1,10 @@
 version: "3.8"
 
 # Docker compose recipe for InvenTree development server
-# - Runs sqlite3 as the database backend
+# - Runs PostgreSQL as the database backend
 # - Uses built-in django webserver
+# - Runs the InvenTree background worker process
+# - Serves media and static content directly from Django webserver
 
 # IMPORANT NOTE:
 # The InvenTree docker image does not clone source code from git.
@@ -11,10 +13,32 @@ version: "3.8"
 # The django server will auto-detect any code changes and reload the server.
 
 services:
+
+    # Database service
+    # Use PostgreSQL as the database backend
+    # Note: This can be changed to a different backend if required
+    inventree-dev-db:
+        container_name: inventree-dev-db
+        image: postgres:13
+        ports:
+            - 5432/tcp
+        environment:
+          - PGDATA=/var/lib/postgresql/data/dev/pgdb
+          # The pguser and pgpassword values must be the same in the other containers
+          # Ensure that these are correctly configured in your dev-config.env file
+          - POSTGRES_USER=pguser
+          - POSTGRES_PASSWORD=pgpassword
+        volumes:
+          # Map 'data' volume such that postgres database is stored externally
+          - src:/var/lib/postgresql/data
+        restart: unless-stopped
+
     # InvenTree web server services
     # Uses gunicorn as the web server
     inventree-dev-server:
         container_name: inventree-dev-server
+        depends_on:
+          - inventree-dev-db
         build:
             context: .
             target: dev