Update ADK doc according to issue #1650 - 2

[adk-bot]

2. Create new documentation for the Parameter Manager integration

Doc file: docs/integrations/parameter-manager.md

Current state:

(File does not exist)

Proposed Change:

Create a new integration page for Parameter Manager.
Add catalog frontmatter (e.g. catalog_title: Parameter Manager, catalog_description: A client for interacting with Google Cloud Parameter Manager.).
Show how to initialize the ParameterManagerClient:

from google.adk.integrations.parameter_manager.parameter_client import ParameterManagerClient

# Using default credentials
client = ParameterManagerClient()

# Or with a service account json string
client = ParameterManagerClient(service_account_json="...")

# Or with an auth token
client = ParameterManagerClient(auth_token="...")

Explain how to retrieve a parameter:

value = client.get_parameter("projects/my-project/locations/global/parameters/my-param/versions/latest")

Reasoning:
A new ParameterManagerClient was introduced to fetch configuration and parameters securely from Google Cloud. Documenting it under integrations makes it discoverable for users building robust cloud-based agents.

Reference: src/google/adk/integrations/parameter_manager/parameter_client.py

[netlify]

✅ Deploy Preview for adk-docs-preview ready!

Name	Link
🔨 Latest commit	fc56e21
🔍 Latest deploy log	https://app.netlify.com/projects/adk-docs-preview/deploys/69e27ccb6042b30008a29a6f
😎 Deploy Preview	https://deploy-preview-1654--adk-docs-preview.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify project configuration.