feat(starknet_getEvent): add transaction_index and event_index to emitted event context

To make creating unique IDs (like used by Voyager, that combines the
block number, the transaction index, and the event index within the transaction)
possible without additional JSON-RPC calls, this change adds two new
indices to the context of emitted events:

- `transaction_index` is the index of the transaction within the block that has
emitted the event.
- `event_index` is the index of the event within the transaction.

Author: kkovaacs

api/starknet_api_openrpc.json

@@ -1114,9 +1114,21 @@
                 "title": "Transaction hash",
                 "description": "The transaction that emitted the event",
                 "$ref": "#/components/schemas/TXN_HASH"
+              },
+              "transaction_index": {
+                "title": "Transaction index",
+                "description": "The index of the transaction in the block by which the event was emitted",
+                "type": "integer",
+                "minimum": 0
+              },
+              "event_index": {
+                "title": "Event index",
+                "description": "The index of the event in the transaction by which it was emitted",
+                "type": "integer",
+                "minimum": 0
               }
             },
-            "required": ["transaction_hash"]
+            "required": ["transaction_hash", "transaction_index", "event_index"]
           }
         ]
       },