Apply env variables on each startup

[ne20002]

Using docker it is very common, that certain configuration values are passed as env variables. It is also common that changing those values result in changed values in the docker container.

Currently the env variables passed to the friendica docker container are only used during install phase and afterwards ignored.

[ne20002]

The env variables for

• the database connection
• the mail setup
• the redis cache

work as expected.

Still need to check the rest of the variables.