Add support for docker secrets

[berndderidder]

It would be great to have support for docker secrets.

Looking at the available environment variables I think these should be added:

• DB_PASSWORD_FILE
• REDIS_PASSWORD_FILE
• MAIL_PASSWORD_FILE
• PUSHER_APP_KEY_FILE
• PUSHER_APP_SECRET_FILE

I had a look at inject.sh and my initial thought was like this:

if [ "$DB_PASSWORD_FILE" != '' ]; then
  value=$(<$DB_PASSWORD_FILE)
  sed -i "s|DB_PASSWORD=.*|DB_PASSWORD=${value}|i" /conf/.env
fi

I think this should be it?

[felin-arch]

I would also welcome this! I dug around to find an alternative but couldn't find one :( I am happy to create a PR for this one.

Any thoughts on the suggestion from @berndderidder ? I also think that would work.

[mingan666]

Are there any plans to implement this enhancement?

[d7415]

#149