hide custom fields section when there are no custom fields created

[Kelsey-Ethyca]

Closes #3545

Code Changes

Updated custom fields list to check a field is created before showing

Steps to Confirm

• verify no custom fields created
• verify the custom list section does not show on the system information or data use tabs
• create a custom field for both system and system: data use
• verify the custom list section does show on the system information or data use tabs with the respective fields you created

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
• For API changes, the Postman collection has been updated

[cypress]

Passing run #2673 ↗︎

0	4	0	0	0
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Details:

Merge a4bc012 into c42a0ac...
Project: fides	Commit: 530f63b613 ℹ️
Status: Passed	Duration: 00:46 💡
Started: Jun 14, 2023 12:14 AM	Ended: Jun 14, 2023 12:15 AM

_{This comment has been generated by cypress-bot as a result of this project's GitHub integration settings.}

[allisonking]

looks good! ⭐