Use single suggest `RepositoryField` instead of multi suggest`RepositoriesField` for lang stats creation UI.

Created by: vovakulikov

Closes https://github.com/sourcegraph/sourcegraph/issues/22042

Background

This PR adds a separate repository field component with suggestions for lang stats insight creation UI. Previously we used multiple repo suggestions for both search-based and lang stats insights, this worked for us because we have a comprehensive validation for the repo field, and by that we didn't allow users to type multiple repositories in lang stats insights creation UI. But to avoid the complexity of supporting use cases for single and multiple repo suggestion fields we have to split this logic (UX may be different from single to multi repo suggests like adding a trailing comma right after a suggestion was selected).

Now we just split these two use cases (sing and multiple repo field) into two separate components RepositoriesField and RepositoryField.