Add myself to istio/wg-networking-maintainers-data-plane team member

[gargnupur]

If you are joining the org, please fill out the template below:

• [X ] I have reviewed the community membership guidelines
• [X ] I have reviewed the contribution guidelines
• [X ] I have enabled 2FA on my GitHub account
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Provide a link to at least one PR that you have successfully pushed to one
of the Istio repos:
istio/proxy#2325 (istio/proxy change for istio/wg-networking-maintainers-data-plane membership)