Implement failover for RPC endpoints in watcher (#506)

* Handle RPC endpoint server errors and switch failover endpoints

* Add config maxNewBlockRetries for switching to failover endpoint

* Upgrade package versions

* Move unknown events removal after event processing for historical sync

* Rename doFailOverEndpoints to switchClients

packages/graph-node/test/utils/indexer.ts

@@ -2,6 +2,7 @@
 
 import assert from 'assert';
 import { DeepPartial, FindConditions, FindManyOptions } from 'typeorm';
+import { providers } from 'ethers';
 
 import {
   IndexerInterface,
@@ -338,4 +339,8 @@ export class Indexer implements IndexerInterface {
   async getFullTransactions (txHashList: string[]): Promise<EthFullTransaction[]> {
     return [];
   }
+
+  switchClients ({ ethClient, ethProvider }: { ethClient: EthClient, ethProvider: providers.BaseProvider }): void {
+    return undefined;
+  }
 }