Allow configurable log levels

[justin8]

I've been using Teslamate for a while, but because I'm running it behind a reverse proxy I get several log lines per second from the healthchecks, making a lot of noise.

It would be great to be able to configure the log level to something other than :info, perhaps through an environment variable?

[djungelorm]

I'm also keen for this feature to be added.

I use a script that queries the index page from teslamate once per minute, to check it is operating correctly. But it generates a lot of noise in the logs with all the successful get requests.