use protobuf content type instead of json for k8s client

[bhavi-koduru]

What this PR does / why we need it:

This MR is a part of effort to elevate single eks cluster performance by migrating the EKS components to use protobuf instead of json.

Modify kubeconfig type to use content type application/vnd.kubernetes.protobuf instead of json for performance gain.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #

[k8s-ci-robot]

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[k8s-ci-robot]

Hi @bhavi-koduru. Thanks for your PR.

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[bryantbiggs]

/ok-to-test

[hakuna-matatah]

/lgtm

[mengqiy]

/lgtm

[bryantbiggs]

FYI - only these folks can approve currently

aws-iam-authenticator/OWNERS

Lines 1 to 5 in 90beff7

	approvers:
	- micahhausler
	- wongma7
	- jyotimahapatra
	- nnmin-aws

[jyotimahapatra]

/lgtm

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: bhavi-koduru, jyotimahapatra

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Needs approval from an approver in each of these files:

• OWNERS [jyotimahapatra]

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