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

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1 out of 2 committers have signed the CLA.
✅ (JTorreG)[https://github.com/JTorreG]
❌ @arpith-f5
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[russokj]

Do we want to mention anything about performance improvements here?

[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