ON-PREM: Use Env Variables to configure vcs.on-premises.properties

Jarek Toro B, thanks for reporting this! We'll provide a fix to support env variables in the VCS config file as well. Meanwhile, below is the workaround I could suggest.

Let's say, we'd like to pass `vcs.dfs.sql_password` property as an env variable (this should work for any other properly as well).

1. Completely remove this property from the `vcs.on-premises.properties` file.
2. Convert its name to the following format: VCS_HOSTING_VCS_DFS_SQL_PASSWORD.
3. Add it to the docker-compose.yml like this: 

services:
    vcs:
        environment:
            VCS_HOSTING_VCS_DFS_SQL_PASSWORD: ${DB_PASSWORD}
            ...

Thank you