Expose state names for checksum_state in Data management API

What does this MR do and why?

Expose the state name (e.g. pending) instead of its integer counterpart in the Data Management REST API.

This was the original intention as you may notice on the field documentation

References

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Enable EE license in your instance.
2. Enable the geo_primary_verification_view feature flag on /rails/features
3. Mae a request to the data management API (http://localhost:3000/api/v4/admin/data_management/upload)
4. Take note of the checksum_state value.

MR acceptance checklist

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Related to #577617