appsettings.Production.json not used

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**Describe the bug**
I somehow just discovered that the appsettings.json should be copied to a appsettings.Production.json file to avoid losing any settings. So I did, and made changes to the appsettings.Production.json file. These however were never used, even after a restart of the docker container.

**To Reproduce**
Steps to reproduce the behavior:
1. Make changes to the appsettings.Production.json file. I changed the Theme from Dark to Light
2. Restart the docker container
3. Logout and reload the webinterface of the server
4. The webinterface still shows the dark theme
5. Make the same change to the appsettings.json file
6. Restart the docker container
7. Reload the webinterface of the server
8. See the page in the light theme

**Remotely Version**
Server: Version: 2021.08.17.1435
Agent: N/A

**Expected Behavior**
The changes should happen when making to the appsettings.Production.json file

**Additional Context**
The server runs in a docker container.

Start by comparing how the Docker deployment loads appsettings.json and appsettings.Production.json when the server starts. Reproduce the reported theme change and container restart, then verify that production settings are applied after the web interface reloads.

Written by the indexing model from the issue text.