Update demo data hook to copy media files (#3441)

* Simplify settings.py / config.py

- get_setting function has been streamlined
- move some functions into config.py

* Spelling fix: IGNORRED is IGNORED

* Ensure yaml is installed as part of docker image

- invoke path is still mucking us around

* Fix broken migration

* Copy media files from demo dataset when installing test data

* Cleanup settings.py

* Fix for configuration file traversal

* Line fix

* Update quickstart guide for docker

* Allow plugin file and plugin dir to be specified in configuration file

* Cleanup config template file

* Allow secret_key information to be provided in configuration file

* Adjust root paths for CI tests

* resolve paths

* Revert paths for CI step

* remove dead code

* Revert configuration variables to old names

- Prevent breaking changes

* Simplify secret key generation

* Fix default timeout for background worker process

* Revert change for customization options

CONTRIBUTING.md

@@ -18,6 +18,7 @@ pip install invoke && invoke setup-dev --tests
 
 ```bash
 git clone https://github.com/inventree/InvenTree.git && cd InvenTree
+docker compose run inventree-dev-server invoke install
 docker compose run inventree-dev-server invoke setup-test
 docker compose up -d
 ```