add log level env variable and update helm

[mikhail-aws]

Note:

• Decouple log-level from dev and prod logging config. Can use different logging levels for both.
• Add env variable to control log level. Introduce few levels: info, debug, error, panic. Default value is info. Still thinking about error and panic logs, probably redundant.
• Add DEV_MODE env variable to enable development logging format.

#530

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[solmonk]

can we update environment.md accordingly and remove GATEWAY_API_CONTROLLER_LOGLEVEL from code and docs?

[mikhail-aws]

@solmonk, removed GATEWAY_API_CONTROLLER_LOGLEVEL from code