NLB-7285: Add dataplane_api_key as an optional

[Naveen-Gopu-F5]

Proposed changes

UseCase
We need dataplane_api_key in authorization header to make api call to Dataplane API. We want to make api_endpoint value as dataplane api which is proxy/copy of nginx plus api that we use as part of NGINXaaS for Azure.

So, when the VMSS (azure scaling group) scales out/scales in, nginx-asg-sync make api calls to dataplane api which updates the upstream servers.

Upstream server update logs

Load balancing incase of 2 instances

Manually scaled to 4 instances

Load balancing after upstream servers updated by nginx-asg-sync

Checklist

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• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

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[Naveen-Gopu-F5]

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

[Naveen-Gopu-F5]

recheck