Dialogflow: Memory leak when a client is created and immediately closed

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#### Environment details

- which product (packages/*): @google-cloud/dialogflow
- OS: All
- Node.js version: 18.16.0
- npm version: 9.5.0
- google-cloud-node version: 5.7.1

#### Steps to reproduce

```javascript
import Dialogflow from '@google-cloud/dialogflow';

const opts = {
servicePath: "dialogflow.googleapis.com",
port: 443,
clientConfig: {
},
fallback: false,
credentials: {
private_key: "...",
client_email: "...",
},
projectId: "...",
scopes: [
"https://www.googleapis.com/auth/cloud-platform",
"https://www.googleapis.com/auth/dialogflow",
],
apiEndpoint: undefined,
};
const conversationProfilesClient = new Dialogflow.ConversationProfilesClient(opts);
await conversationProfilesClient.close();
```

The constructor creates `operationsClient` which tries to connect and registers itself in channelz, but the ctor doesn't assign anything to `conversationProfilesStub`, so `close` is no-op. We're left with a memory leak in channelz.

Our use-case was creating this object for calling `projectLocationConversationProfilePath` (why are these functions not static?).