fix(gcp-marketplace): make the listing deployable and document it

[aelmanaa]

This pull request introduces several documentation and configuration improvements for deploying Chainlink CCV Cells, with a particular focus on clarifying secrets management, service account setup, and support for different Gateway API route kinds in GCP Marketplace deployments. The changes aim to improve the clarity and flexibility of deployment instructions, especially for users leveraging Google Cloud Marketplace and various cloud secret management backends.

Key changes include:

Documentation and Deployment Guidance

• Added clear instructions for users deploying via Google Cloud Marketplace, directing them to the appropriate starting point and clarifying when to switch back to the main runbook.
• Expanded documentation on the use of resolver addresses for verifier configuration, including consequences of misconfiguration and troubleshooting tips.
• Improved explanations of service account creation and usage, including when to set create: true or false, and clarified the implications for GCP Marketplace users.
• Added detailed guidance on Workload Identity for GCP, distinguishing between direct binding and impersonation, with recommendations and example commands.
• Enhanced troubleshooting section with more precise error scenarios and outcomes for secret mounting and permissions.

Secret Management and Configuration

• Clarified that the dbUrlRemoteRef for the verifier's bootstrap secret is only needed when keystoreBackend is set to postgres, both in documentation and in the Helm chart templates. [1] [2] [3] [4]
• Documented the two required roles for the verifier's KMS keystore backend on Google Cloud and the need to reference the HSM-protected key correctly.
• Improved descriptions in GCP Marketplace schemas for secrets, making explicit what each secret contains and how it is used. [1] [2] [3]

Gateway API Route Kind Flexibility

• Added support for selecting between GRPCRoute and HTTPRoute for the aggregator's Gateway API resource, with schema validation, documentation, and template logic to handle both kinds. This is important for compatibility with GKE's managed Gateway, which only supports HTTPRoute. [1] [2] [3] [4]

Schema and Validation Updates

• Updated required fields in the GCP Marketplace schema to ensure all necessary parameters are provided, especially for route configuration. [1] [2]
• Enhanced the signer_address field to allow the value auto for automatic key generation on first deployment, with improved documentation.

These changes collectively improve the deployment experience, reduce the risk of misconfiguration, and ensure compatibility with a broader range of cloud environments and Gateway controllers.

[github-actions]

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