vertex-sdk: Add gcp-labels to llm calls

[mktce]

When using gemini models via vertex API, it is possible to add gcp labels to API calls (https://cloud.google.com/vertex-ai/generative-ai/docs/multimodal/add-labels-to-api-calls). It would be very helpful, if the same was possible for anthropic calls via vertex API.

[RobertCraigie]

Thanks for the request, what would you want the SDK interface to be?

[mktce]

I could imagine, that analogous to Google's generateContent endpoint (see https://cloud.google.com/vertex-ai/docs/reference/rest/v1/projects.locations.endpoints/generateContent), the MessageCreateParamsBase gets a new property labels that can be used on each create-call, like:

const result = await client.messages.create({
    messages: [{role: 'user', content: 'Hey Claude!'}],
    model: 'claude-3-5-sonnet-v2@20241022',
    labels: {
        'component': 'frontend',
        'team': 'research'
    }
});