Update the GCP docs to their own page

**What content needs to be created or modified?**

We need a page like the "Authenticating to Azure/AWS" pages but for GCP. We need to take what was started [here](https://github.com/dapr/docs/pull/4592) by @antontroshin and bring it out into its own page to simplify the GCP component docs. Today, all the components in Dapr except for the Firestore component support implicit credentials.


**Describe the solution you'd like**

**Where should the new material be placed?**
https://docs.dapr.io/developing-applications/integrations/

under a new page called "GCP"

**The associated pull request from dapr/dapr, dapr/components-contrib, or other Dapr code repos**

**Additional context**