Add : Shubham Gupta to maintainer

[shubham-cmyk]

Why is this pull request needed and what does it do?

Add @shubham-cmyk to mainatiner

Which issues (if any) are related?

https://github.com/coredns/helm/issues/96

Checklist:

• [ ] I have bumped the chart version according to versioning.
• [ ] I have updated the chart changelog with all the changes that come with this pull request according to changelog.
• [ ] Any new values are backwards compatible and/or have sensible default.
• [ ] I have signed off all my commits as required by DCO.

Changes are automatically published when merged to main. They are not published on branches.

Note on DCO

If the DCO action in the integration test fails, one or more of your commits are not signed off. Please click on the *Details* link next to the DCO action for instructions on how to resolve this.

[mrueg]

Please add yourself here as well: https://github.com/coredns/helm/blob/master/charts/coredns/Chart.yaml#L14 (and bump the patch version of the Chart)

[shubham-cmyk]

@mrueg Done