[repo] enforce classnames import name format via eslint rule

[soniadeveloper]

Summary

The classnames import was updated so each instance of it in every file has the same import name. For example, whenever classnames is imported it should be imported as
import classnames from 'classnames'
However, there should be an ESLint rule that produces an error when an import uses a name that isn't approved in order to maintain consistency.

Additional context
See issue #799

[soniadeveloper]

According to this issue: import-js/eslint-plugin-import#1143 there is a linting rule in the making that will accomplish what we need