Replace JSON/YAML marshaling with just YAML marshaling

[eyal-mor]

Original Author: @dkirillov

Summary

The readConfigFile function is able to read both YAML and JSON file. Using a switch-statement it picks the correct class to unmarshal data with.

This switch statement can be removed in favor of using just YAML (from gopkg.in/yaml.v3) to unmarshal things.

Motivation

Reduce and make cleaner code.

Describe alternatives you've considered

N/A

Additional context

An attempt was made, however, started to look like a rabbit hole with the errors that would come up (see screenshot below).

It should be possible, just would need to have a separate PR for clarity.