add assigned systems to user management table

[eastandwestwind]

Closes #2861

Code Changes

• Adds column to show number of assigned systems in user management table

Steps to Confirm

• Add new users with varying amounts of systems. Confirm the number of systems assigned is reflected in user management table.

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

Description Of Changes

Write some things here about the changes and any potential caveats

[cypress]

Passing run #1066 ↗︎

0	3	0	0	0
⚠️ You've recorded test results over your free plan limit. Upgrade your plan to view test results.

Details:

Merge 0072569 into 22349a8...
Project: fides	Commit: 1615568206 ℹ️
Status: Passed	Duration: 00:50 💡
Started: Mar 29, 2023 12:52 PM	Ended: Mar 29, 2023 12:53 PM

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

[allisonking]

we should probably add a test case for this in cypress, too :)

[eastandwestwind]

Back over to you @allisonking ! I've added a cypress test and addressed your comments

[allisonking]

nice work 💯