[BUG] UI don't use shared volume for configs when using Docker

[fl0ppy-d1sk]

Description
At the moment, we use a shared volume between BW and UI mounted on /etc/nginx for sharing configurations. The problem is that BW is overwriting the configurations when it restarts and so all configurations are lost.

How to reproduce

1. Follow the steps in the documentation for the Docker integration : https://docs.bunkerweb.io/1.4/web-ui/#installation
2. Do some config on the UI
3. Restart the BW container : all configs are lost

Idea
Use the ApiCaller._send_files method to send configs each time it's needed (just like here).