ADD: Refactor providers and explorers implementation for @next release

[mikewyszinski]

overview

Currently the providers(APis to fetch live information and broadcast txs) and Explorers are hard wired into each client.

This is suboptimal for the following reasons:

1. selecting a provider(sochain,haskoin,etherscan, etc) should be up to the user of the library
2. providers should allow users to configure paid services (paid blockchair, paid infura node, etc)
3. by default the library should support fall back providers in coase 1 providers is down
4. it should be easy for users to develop their own provider and plug it into the library

Work to do

• [ ] Prototype explorers & providers with xchain-bitcoin
• [ ] Prototype explorers & providers with xchain-ethereum
• [ ] Support configurable Providers & Explorers for 3rd party functions
• [ ] For each Chain, default to free, reliable Providers & Explorers
• [ ] move all providers/explorers into xchain-client, since several bproviders support more that one chain BTC/BCH, etc

Example of finished product

1. install the right libraries (npm,yarn,pnpm,etc)

   # install the required base lib
   yarn add @xchainjs/xchain-client 
   
   # install chains you want to interact with
   yarn add @xchainjs/xchain-bitcoin @xchainjs/xchain-ethereum 
   

2. Setup the client libs

   
   import { Providers, Explorers } from '@xchainjs/xchain-client';
   
   //import chains you want  
   import { BtcClient } from '@xchainjs/xchain-bitcoin';
   import { EthClient } from '@xchainjs/xchain-ethereum';
   
   const network = 'testnet'
   const phrase = 'atom green various power must another rent imitate gadget creek fat then'
   
   //ETHEREUM Config
   const ethConfig = {
       network,
       phrase,
       explorer: Explorers.ETH.ETHERSCAN,
       providers: {
           // all methods take an array of providers, they will be invoked in order until one returns a success 
           getBalance:         [Providers.ETH.BLOCKCHAIR,Providers.ETH.ETHERSCAN],
           getTransactions:    [Providers.ETH.BLOCKCHAIR,Providers.ETH.ETHERSCAN],
           getFees:            [Providers.ETH.ETHPLORER, Providers.ETH.ETHERSCAN],
           transfer:           [Providers.ETH.ETHERSCAN],
       }
   }
   const ethClient = EthClient(ethConfig)
   
   //BITCOIN Config
   const btcConfig = {
       network,
       phrase,
       explorer: Explorers.BTC.BLOCKSTREAM,
       providers: {
           // all methods take an array of providers, they will be invoked in order until one returns a success 
           getBalance:         [Providers.BTC.BLOCKCHAIR, Providers.BTC.SOCHAIN, Providers.BTC.HASKOIN ],
           getTransactions:    [Providers.BTC.BLOCKCHAIR, Providers.BTC.SOCHAIN, Providers.BTC.HASKOIN ],
           getFees:            [Providers.BTC.BLOCKCHAIR, Providers.BTC.HASKOIN],
           transfer:           [Providers.BTC.BLOCKCHAIR],
       }
   }
   
   const btcClient = BtcClient(btcConfig)
   
   //overide a config with a provider 
   const apiKey = '12345'
   const blockchairBtc = new Providers.BlockChair({apiKey, chain: 'BTC'})
   //use paid blockchair and if we run out of credits, fall back to public api endpoints
   btcClient.config.providers.getBalance = [blockchairBtc, Providers.BTC.SOCHAIN, Providers.BTC.HASKOIN ]