WIP: Convert most user management views' tests to pytest format

[rebeccacremona]

This work was started during the Q3 housekeeping cycle, but was not finished.

Still to do:

• test_org_export_user_list
• test_sponsored_user_export_user_list
• test_create_and_delete_user
• All the tests in "### ADDING NEW USERS TO ORGANIZATIONS ###"
• All the tests in "### ADDING EXISTING USERS TO ORGANIZATIONS ###"
• All the tests in "### VOLUNTARILY LEAVING ORGANIZATIONS ###"
• All the tests in "### REMOVING USERS FROM ORGANIZATIONS ###"
• All the tests in "### ADDING NEW USERS TO REGISTRARS AS SPONSORED USERS ###"
• All the tests in "### ADDING EXISTING USERS TO REGISTRARS AS SPONSORED USERS ###"
• All the tests in "### TOGGLING THE STATUS OF SPONSORSHIPS ###"
• All the tests in "### ADDING NEW USERS TO REGISTRARS AS REGISTRAR USERS) ###"
• All the tests in "### ADDING EXISTING USERS TO REGISTRARS ###"
• All the tests in "### REMOVING REGISTRAR USERS FROM REGISTRARS ###"
• All the tests in "### ADDING NEW USERS AS ADMINS ###"
• All the tests in "### ADDING EXISTING USERS AS ADMINS ###"
• All the tests in "### REMOVING USERS AS ADMINS ###"

Not in scope:

• Any tests of filters. those are going to be a pain to convert, as long as JSON fixtures are still being installed. (edit: I added a helper to delete interfering JSON fixtures... but I still think those should all be done at once... may be there is a much more efficient way to test)
• "### SIGNUP" (should be their own file)
• "### PASSWORD RESETS ###" (should be elsewhere)

[codecov]

Codecov Report

❌ Patch coverage is 99.52607% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 70.64%. Comparing base (8fc6741) to head (70eb0ff).
⚠️ Report is 5 commits behind head on develop.

Files with missing lines	Patch %	Lines
perma_web/conftest.py	99.50%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #3621      +/-   ##
===========================================
+ Coverage    69.47%   70.64%   +1.16%     
===========================================
  Files           58       58              
  Lines         7837     8035     +198     
===========================================
+ Hits          5445     5676     +231     
+ Misses        2392     2359      -33     

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