Example subgraph, ethCall test to drive implementation (#18)

* Setup example subgraph.

* Implement eth_call in subgraph.

* eth-call test stub

Co-authored-by: nabarun <nabarun@deepstacksoft.com>

packages/graph-node/test/contracts/Example.sol

@@ -0,0 +1,10 @@
+pragma solidity >=0.4.22 <0.8.0;
+
+contract Example  {
+    event Test(string param1, uint param2);
+
+    function getMethod() public view virtual returns (string memory)
+    {
+        return 'test';
+    }
+}