feat(onramp): adding onramp buy options endpoint

[geekbrother]

Description

This PR adds the new endpoint for getting buy options for the onramp payments from the CB payment options endpoint.

• /v1/onramp/buy/options GET parameters:
  • projectId - project ID
  • country - ISO 3166-1 two-digit country code string representing the purchasing user’s country of residence, e.g., US.
  • subdivision (optional) - ISO 3166-2 two-digit country subdivision code representing the purchasing user’s subdivision of residence within their country, e.g. NY. Required if the country=“US” because certain states (e.g., NY) have state specific asset restrictions.

The new endpoint response object contains the following fields:

• paymentCurrencies - List of supported fiat currencies that can be exchanged for crypto on CBPay in the given location. Each currency contains a list of available payment methods, with min and max transaction limits for that currency id.
• purchaseCurrencies - List of available crypto assets that can be bought on CBPay in the given location.

Context of this requirement: https://walletconnect.slack.com/archives/C03SCF66K2T/p1706780083868789?thread_ts=1706744422.369399&cid=C03SCF66K2T

How Has This Been Tested?

1. New integration test included with this PR.

2. Manual.

• Start the server locally: cargo run.
• Run the following curl request: curl -v 'http://localhost:3000/v1/onramp/buy/options?projectId=xxx&country=US' | jq .

Due Diligence

• Breaking change
• Requires a documentation update
• Requires a e2e/integration test update