refine dataset_type validation

[kburke]

For initial release, new values for dataset_type on a Dataset entity are limited to a Dataset type recognized by UBKG, possibly followed by a single space and square brackets with non-validated content.

Revise the error message if exactly one space is the appropriate requirement, or revise the regular expression for validation if we are flexible about the number of spaces. This will help avoid issues like: #586

If new constraints for validating content inside the square brackets are available, this work can be done with that work.
https://github.com/hubmapconsortium/manual-data-ingest/issues/268#issuecomment-1848614060

[yuanzhou]

9/23/2024 Notes from Bill

<valid_dataset_type> [*] needs to remain as a valid value for HIVE processed dataset types. We don’t have a specific list of

• a) individual processed dataset types or
• b) what goes inside of the brackets.