add log level configuration via environment

[apidkaminnyi]

Fixes #5

Add an ability to override the log level with env variable SECRETS_MANAGER_LOG_LEVEL

[pingvinen]

Hi @apidkaminnyi

Thank you for the contribution :) Do you feel up for updating the code to actually use the log level as well? Currently, the logging is done using console.log (and the semantic overloads), but console.log does not - to my knowledge at least - support "filtering" by log level.

Since this is a dev-box tool, the requirements are pretty loose. While I do like having less code to maintain, I also see value in not adding dependencies when the solution can be done in very few lines of code. My suggestion would be to write a small wrapper around console.log. That will keep it simple and will be 1 fewer dependency to keep up to date with.