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

Checklist

Before merging a pull request, run through this checklist and mark each as complete.

• I have read the contributing guidelines
• I have signed the F5 Contributor License Agreement (CLA)
• I have rebased my branch onto main
• I have ensured my PR is targeting the main branch and pulling from my branch from my own fork
• I have ensured that the commit messages adhere to Conventional Commits
• I have ensured that documentation content adheres to the style guide
• If the change involves potentially sensitive changes¹, I have assessed the possible impact
• 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
• If applicable, I have updated README.md and CHANGELOG.md

Footnotes

1. Potentially sensitive changes include anything involving code, personally identify information (PII), live URLs or significant amounts of new or revised documentation. Please refer to our style guide for guidance about placeholder content. ↩

[arpith-f5]

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

[amudukutore]

@arpith-f5 - Thanks for making these changes. These instructions will be very useful as we guide customers to switch over to the new metrics mechanism.

[JTorreG]

Suggested change

	## Overview
	NGINXaaS previously supported monitoring using [Custom Metrics](https://learn.microsoft.com/en-us/azure/azure-monitor/metrics/metrics-custom-overview). Custom metrics is a preview feature in Azure and support for it will be dropped in the future. We have added support for Platform metrics which is the Azure recommended way for monitoring resources, we strongly recommend you to migrate your deployments monitoring to use Platform metrics to take advantage of reduced latency and higher reliability.
	## Overview
	NGINXaaS for Azure previously supported monitoring using [Custom Metrics](https://learn.microsoft.com/en-us/azure/azure-monitor/metrics/metrics-custom-overview). Custom metrics is a preview feature in Azure and support for it will be dropped in the future. We have added support for Platform metrics, which is the Azure recommended way for monitoring resources; we strongly recommend you migrate your deployments monitoring to use Platform metrics to take advantage of reduced latency and higher reliability.

[JTorreG]

This PR has been merged with some style issues I was providing feedback on.

I will open a new PR with my suggestions.