Allow purchase of crypto assets via Coinbase Pay

[justindg]

Allow users to purchase crypto assets via Coinbase Pay.

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Endpoint:
https://pay.coinbase.com/buy/select-asset

Parameters:
appId : string - Provided by Coinbase Pay team, check discord for valid AlphaWallet app ID.
destinationWallets : array - See below.

Destination Wallets Parameters:
address : string - Destination address where the purchased tokens will be sent.
blockchains : string array - List of enabled blockchains, available values*: ethereum, solana, avalanche-c-chain
assets : string array - List of tokens that will be displayed to the user in the succeeding screen

• Seems only ethereum blockchain is relevant to AlphaWallet

Upon testing, there are two ways we could utilize this API.

1. Select from a list of tokens in the ethereum network:

https://pay.coinbase.com/buy/select-asset?appId=<APP_ID>&destinationWallets=[{"address": "<WALLET_ADDRESS>","blockchains":["ethereum"]}

2. Directly purchase a token; this will skip the token selection screen:

https://pay.coinbase.com/buy/select-asset?appId=<APP_ID>&destinationWallets=[{"address": "<WALLET_ADDRESS>","assets":["ETH"]}

Requirements to test this feature:

1. Verified Coinbase account - may include ID verification and linked payment info depending on the country of origin.

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Sample flow:

Screen_Recording_20220818-145949_AlphaWallet.mp4