fix(openclaw): use ADC instead of service account keys (#207)

[Sabina8205]

Summary

Updates the OpenClaw Agent Platform migration guidance to use secure Application Default Credentials (ADC) instead of downloaded service-account keys.

Changes

• Removes service-account key creation and copying instructions.
• Removes guidance to disable the organization policy that blocks key creation.
• Uses the attached service account automatically on Compute Engine VMs.
• Documents gcloud auth application-default login for workstations.
• Recommends Workload Identity Federation for non-Google-Cloud hosts.
• Removes GOOGLE_APPLICATION_CREDENTIALS from the OpenClaw configuration example.
• Removes the no-longer-needed project-number lookup, including its incorrect VM metadata endpoint.

Validation

• Ran git diff --check.

Fixes #207

[google-cla]

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[kumar-dhanagopal]

Hi @Sabina8205, thank you for this contribution! As explained in https://github.com/google/skills/blob/main/CONTRIBUTING.md#how-you-can-help, we're not accepting PRs for this repo currently. Your suggestion is valuable though, and we'd like to make sure that we internally triage it. Please feel free to post it as an issue in https://github.com/google/skills/issues.

[Sabina8205]

Thank you for the clarification. I understand, and I appreciate that the existing issue #207 will be internally triaged.