sig-storage: add team repo permissions for external-snapshot-metadata repo

[Priyankasaggu11929]

Ref: #4874

/assign @kubernetes/sig-storage-leads

cc: @kubernetes/owners

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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[Priyankasaggu11929]

@xing-yang — @carlbraganza and @PrasadG193 will need requesting new org membership before the tool allows them to add to a GH team.

 --- FAIL: TestAllOrgs (0.08s)
    config_test.go:268: The following members of team external-snapshot-metadata-maintainers are not Kubernetes CSI org members: carlbraganza, prasadg193
    config_test.go:268: The following members of team external-snapshot-metadata-admins are not Kubernetes CSI org members: carlbraganza, prasadg193 

Do you suggest to (i) move ahead with this PR & add @carlbraganza, @PrasadG193 later once the org membership requests are processed, or (ii) wait?

[xing-yang]

@Priyankasaggu11929 Sorry, I missed this earlier. Please go ahead with this PR and we can add @carlbraganza, @PrasadG193 later. Thanks!

[Priyankasaggu11929]

Thanks @xing-yang.

I've refreshed the PR. Ready to lgtm/approve.

[xing-yang]

/lgtm