scenarios/grpc: add simple search example

It does what it claims, however, it may be adjusted to real requirements in the
future. Controlled by a number of iterations and number of virtual users.
Searches for objects with `test=test` attributes. Closes #90.

Run example:
```
▶ ./xk6-neofs run -e i=200 -e vu=1 -e cid=FB6UeNbx65iHuNKNbGsb2xHxooU7kXangaUxv9P6h9uW -e GRPC_ENDPOINT=s01.neofs.devenv:8080 scenarios/grpc_search.js
```

Signed-off-by: Pavel Karpy <[email protected]>

scenarios/grpc_search.js

@@ -0,0 +1,35 @@
+import { check } from 'k6';
+import native from 'k6/x/neofs/native';
+
+const dial_timeout = 5
+const stream_timeout = 15
+const predefined_private_key = '' // usually no need for search requests in load tests
+const grpc_client = native.connect(__ENV.GRPC_ENDPOINT, predefined_private_key, dial_timeout, stream_timeout);
+const container = __ENV.cid
+
+export const options = {
+    scenarios: {
+        system_write: {
+            executor: 'shared-iterations',
+            vus: __ENV.vu,
+            iterations: __ENV.i,
+            exec: 'search',
+            maxDuration: (24*365*100).toString()+"h", // default is 10m and this load is designed to be controlled by iterations only
+            gracefulStop: '30s',
+        },
+    },
+};
+
+export function search() {
+    let res = grpc_client.search(container, [{
+        key: "test",
+        operation: "STRING_EQUAL",
+        value: "test"
+    }])
+    check(res, {
+            'search': (r) => {
+                return r > 0;
+            }
+        }
+    )
+}