Draft: Add otel-resource-attr as a supported directive in NGINXaaS GCP

[f5cziegler]

Left as draft until code MR is merged

Proposed changes

This commit adds the otel-resource-attr as a supported directive for the NGINXaaS GCP project and links to the public documentation for the directive. This follows the format for the rest of the directives listed.

Checklist

Before sharing this pull request, I completed the following checklist:

• I read the Contributing guidelines
• My branch adheres to the Git conventions
• My content changes adhere to the F5 NGINX Documentation style guide
• I have waited to ensure my changes pass tests, and addressed any discovered issues

[github-actions]

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2 out of 3 committers have signed the CLA.
✅ (JTorreG)[https://github.com/JTorreG]
✅ (travisamartin)[https://github.com/travisamartin]
❌ @f5cziegler
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[JTorreG]

Hi @f5cziegler , is this PR waiting on anything specific?

[github-actions]

This PR is stale because it has been open 90 days with no activity. Remove the stale label or add a comment to keep it open. If you do not take action, this will be closed in 10 days.