Log if DAB_ENVIRONMENT variable is found and used

[yorek]

During the startup it would useful to log if the DAB_ENVIRONMENT variable is used and that value is found in there. I would help to make sure misspelled values or variable name (for example: DAB_ENVIROMENT, with a missing "N") are easily detected and corrected right away :)

[abhishekkumams]

This is completed as part of #1497