Simplify usage (e.g. by adding API, CLI)

[patrislav]

Abstract

Currently, this project can only be used as a library that is imported into an existing Go program. This heavily limits the ease of use and adoption. While having it be used as a library is our main use case, we should allow for other methods as well.

Implementation details

The proposal is to add a few flexible building blocks that the users could use (or not) depending on needs:

1. An HTTP handler that estimates the costs of a TF plan that can be easily added into any Go server
2. A simple API whose entire purpose would be to expose the handler above, allowing the users to start the API and not have to write a single line of code
3. CLI that is able to send requests to the HTTP handler above (either included in the simple API or any other Go server), parse the cost estimation result and print it out

These three components should be able to cover most use cases.