replace interface{} with string for zms-cli import operations

[havetisyan]

Description

addresses zms-cli panic with:

panic: interface conversion: interface {} is map[string]interface {}, not map[interface {}]interface {}

error message when updating a domain

Contribution Checklist:

• The pull request does not introduce any breaking changes
• I have read the contribution guidelines.
• Create an issue and link to the pull request.

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