Update NGINXaaS documentation for native-metrics integration

[arpith-f5]

Proposed changes

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Problem: Documentation change for NGINXaaS to add info about native-metrics integration

Solution: Explain the approach you took to implement the solution, highlighting any significant design decisions or
considerations.

Testing: Describe any testing that you did.

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Closes #ISSUE

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[github-actions]

✅ All required contributors have signed the F5 CLA for this PR. Thank you!
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[russokj]

Looks good - only problem is I can't approve - @jputrino
(maybe because it's still in draft mode)

[JTorreG]

@arpith-f5 please move it out of draft when it is ready for review

[arpith-f5]

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