Setting OVERWRITE_SETTING_theme-custom-css env variable doesn't take effect

Description:

I wanted to set custom css without need to do this from UI. Similarly as other settings OVERWRITE_SETTING_theme-custom-css was set in env variables, but after starting rocket chat in Administration -> Layout -> custom Css value provided in env variable is not set.
No related errors in log.

Steps to reproduce:

1. Add OVERWRITE_SETTING_theme-custom-css: "test content" to environment section of rocket chat compose.yml file.
2. Start RocketChat
3. Go to Administration -> Layout -> custom Css

Expected behavior:

Custom css value is "test content"

Actual behavior:

Custom css value is empty

Server Setup Information:

• Version of Rocket.Chat Server: 6.1.6
• Operating System: Ubuntu
• Deployment Method: docker
• Number of Running Instances: 1
• DB Replicaset Oplog: Enabled
• NodeJS Version: 14.21.2 - x64
• MongoDB Version: wiredTiger

Client Setup Information

• Desktop App or Browser Version: Mozilla FF
• Operating System: Ubuntu

Additional context

It's worth to mention that other similar settings like "OVERWRITE_SETTING_Custom_Script_On_Logout" are passed correctly.
Also setting theme-custom-css via rest api works correctly.
Seems that issue is caused by '-' character in setting name and because of that it cannot be passed via env variables.

Relevant logs:

No relevant logs found.

Start by tracing Rocket.Chat's environment-variable setting override handling, comparing theme-custom-css with Custom_Script_On_Logout and the REST API path. Reproduce the issue with the compose environment described in the report; done when OVERWRITE_SETTING_theme-custom-css populates the custom CSS setting and the behavior is covered by a regression check.