chore: import upstream snapshot with attribution

docs/en/integrations/cloudmonitoring/source.md

@@ -0,0 +1,47 @@
+---
+title: "Cloud Monitoring Source"
+type: docs
+linkTitle: "Source"
+weight: 1
+description: >
+  A "cloud-monitoring" source provides a client for the Cloud Monitoring API.
+no_list: true
+---
+
+## About
+
+The `cloud-monitoring` source provides a client to interact with the [Google
+Cloud Monitoring API](https://cloud.google.com/monitoring/api). This allows
+tools to access cloud monitoring metrics explorer and run promql queries.
+
+Authentication can be handled in two ways:
+
+1.  **Application Default Credentials (ADC):** By default, the source uses ADC
+    to authenticate with the API.
+2.  **Client-side OAuth:** If `useClientOAuth` is set to `true`, the source will
+    expect an OAuth 2.0 access token to be provided by the client (e.g., a web
+    browser) for each request.
+
+## Available Tools
+
+{{< list-tools >}}
+
+## Example
+
+```yaml
+kind: source
+name: my-cloud-monitoring
+type: cloud-monitoring
+---
+kind: source
+name: my-oauth-cloud-monitoring
+type: cloud-monitoring
+useClientOAuth: true
+```
+
+## Reference
+
+| **field**      | **type** | **required** | **description**                                                                                                                                |
+|----------------|:--------:|:------------:|------------------------------------------------------------------------------------------------------------------------------------------------|
+| type           |  string  |     true     | Must be "cloud-monitoring".                                                                                                                    |
+| useClientOAuth | boolean  |    false     | If true, the source will use client-side OAuth for authorization. Otherwise, it will use Application Default Credentials. Defaults to `false`. |