[Feat] Parse a YAML file for config

The yaml file for now should allow 2 fields only
* A list of urls of backends
* Frequency, basically an integer which determines the frequency at which the healthcheck will be called.

To implement it, add a new folder inside pkg to parse a yaml and return a struct.

Start by inspecting the Go module and the existing pkg layout, then identify how configuration is represented elsewhere. Add a new pkg folder for YAML parsing that returns a struct containing backend URLs and the health-check frequency; done means a YAML file with those two fields can be parsed successfully.

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