NGINXaaS Platform metric migration

[arpith-f5]

Proposed changes

Write a clear and concise description that helps reviewers understand the purpose and impact of your changes. Use the
following format:

Problem: Add instructions for customer to migrate from custom metric to platform metrics for NGINXaaS

Solution: created a new page with instructions.

Testing: Local testing.

Please focus on (optional): If you any specific areas where you would like reviewers to focus their attention or provide
specific feedback, add them here.

If this PR addresses an issue on GitHub, ensure that you link to it here:

Closes #ISSUE

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• If applicable, I have added tests that prove my fix is effective or that my feature works
• I have ensured that existing tests pass after adding my changes
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[arpith-f5]

I have hereby read the F5 CLA and agree to its terms