refactor: general improvements in sdk codebase (restored)

[nicolasribeiroo]

Summary

refactor in the entire code-base structure, support for more api features and more!

Why

since this code didn't received any update in 2 years, the sdk does not support some api features (such /store, /withdraw, etc.). the code also lacks very clear documentation and resource modules do not match the other sdks (e.g., abacate.billings.create() - AbacatePay.Resources.Billing.create()).

the official package is also not available in hex.pm. in this pr i will be configuring the files for release.

What changed

• Updated deps
• Add Coupon, Product, Store, Withdraw, Pix and TrustMRR features
• Added more detailed documentation for each type
• Added CI
• Add new top-level resource modules to align with other SDKs (AbacatePay.Resources.Customers to AbacatePay.Customers)
• Instead of instantiating a HTTP Client, you only need to configure the API keys via the Config file. well take care of everything else for you
• Switched from HTTPoison to Finch. Finch is more minimal and performant.
• Change the semantic of the api params in SCREAMING_SNAKE_CASE/camelCase to snake_case to follow the common naming semantics in Elixir.
• Files configured for release the package in hex.pm
• Add nimble_options for validating function options in structs

Breaking changes

• Yes
• No

Checklist

• Docs updated
• CI passing
• I followed the CONTRIBUTING guidelines
• I added or updated tests (if applicable)

[albuquerquesz]

LGTM!!