Add utilities for preparing Conversion payments

[MantisClone]

Problem

Builders have experienced difficulty integrating Conversion, Swap-to-pay, and Swap-to-conversion payments due to the lack of utilities or templates for preparing transactions.

Solution

Open source the utilities that Request Finance uses to prepare Conversion, Swap-to-pay, and Swap-to-Conversion payments.
Add utilities to the RN SDK for preparing Conversion payments.

Definition of Done

• Ask Request Finance for permission to open-source their utils - Private Slack Conversation - Approved ✅
• Copy the Request Finance utilities to the requestNetwork repo and make them easy to call. Unable to reuse them.
• Add to the RN SDK the utilities for preparing Conversion payments created in [invoicing template] Support Conversion Payments web-components#76

Reference

These are the utilities written by Request Finance. We've since discovered that they're not as reusable as originally thought.

• https://github.com/RequestNetwork/invoicing/blob/master/src/features/payment/utils/payment-settings/getConversionPaymentValues.ts
• https://github.com/RequestNetwork/invoicing/blob/master/src/features/payment/utils/payment-settings/getSwapPaymentValues.ts
• https://github.com/RequestNetwork/invoicing/blob/master/src/features/payment/utils/payment-settings/getSwapWithConversionPaymentValues.ts
• https://github.com/RequestNetwork/invoicing/blob/master/src/lib/conversion.tsx
• https://github.com/RequestNetwork/invoicing/blob/master/src/lib/chainlink.ts

[MantisClone]

I'm reducing the scope by removing swap-to-conversion because we discovered that swap-to-conversion is not supported by the SDK at all. Adding swap-to-conversion to the SDK is a larger task and should be tracked separately. I created #1469 to track.

[MantisClone]

@rodrigopavezi added Conversion to Request Invoicing in RequestNetwork/web-components#76. While doing so, he discovered that the utilities from Request Finance are not as easy to reuse as @MantisClone originally thought. So he ended up implementing his own utilities for preparing Conversion payments.

The scope of this task has changed to formalizing the Conversion utilities that @rodrigopavezi developed by adding them to the RN SDK.