Poll classification results for datasets

[allisonking]

Closes https://github.com/ethyca/fidesplus/issues/402

Code Changes

• Pull polling code into a common hook
• Use hook in dataset classification flow

Steps to Confirm

• Make sure data flow classification still works by using the data flow scanner and waiting for classification results.
• Make sure dataset classification still works by going to localhost:3000/dataset with the fidesplus backend. Create a dataset by connecting to a database (i.e. postgresql://postgres:[email protected]:5432/fides). Wait for classification without refreshing the page. This can take ~15 minutes. If you open the network tab, you should see it checking the classification results every 3 seconds

Pre-Merge Checklist

• All CI Pipelines Succeeded
• Documentation:
  • documentation complete, PR opened in fidesdocs
  • documentation issue created in fidesdocs
• Issue Requirements are Met
• Relevant Follow-Up Issues Created
• Update CHANGELOG.md

Description Of Changes

Write some things here about the changes and any potential caveats

[TheAndrewJackson]

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