[Go] Refactor the entrypoint and cli packages

[olena-zmiiova]

Linked issue: #43

The cli packages has a validation for arguments received from the entrypoint, so they should be refactored in one scope:

1. The args validation code should be easier to read and understand.
2. Remained cyclop linter issues should be resolved.
3. Reconsider the naming of arguments.
4. Add logging.
5. Add output to a user after a successful run.
6. Improve error processing.
7. Recheck & update documentation.
8. Update UTs, checking if they can be improved with gomega and ginkgo libs.

[olena-zmiiova]

PRs are merged #49, #50, closing an issue.