agents: fix grpc insecure opt initialization

`OtlpGrpcClientOptions.use_ssl_credentials` is not initialized by
default to `false` as it happens with all their children. Make sure it
is otherwise it can produce undesired behaviour.

PR-URL: #247
Reviewed-By: Rafael Gonzaga <[email protected]>
PR-URL: #245

Author: santigimeno

agents/grpc/src/grpc_agent.cc

@@ -1037,8 +1037,8 @@ int GrpcAgent::config(const json& config) {
       opts.endpoint = endpoint;
       opts.metadata = {{"nsolid-agent-id", agent_id_},
                        {"nsolid-saas", saas()}};
+      opts.use_ssl_credentials = !insecure;
       if (!insecure) {
-        opts.use_ssl_credentials = true;
         if (!custom_certs_.empty()) {
           opts.ssl_credentials_cacert_as_string = custom_certs_;
         } else {