Fix duplicate user errors encountered in Django admin

[rnovak338]

Addresses #4878

We have encountered an issue with duplicate users when it comes to granting tribal access. We realized that duplicate users are inevitable, and here's why.

Login.gov does not allow multiple accounts to share one email address. However sometimes, a user will delete their account on Login.gov and start a new account. When this user logs into the FAC with a new account (but the same email), we have no way of guaranteeing what the situation is, other than that Login.gov is giving us a unique username... therefore we create a new (but duplicated) user. Logically, the most recently active user (going off of last_login) is the most up-to-date account.

This PR makes some fixes in Django admin to recognize this case and continue to operate without failure.

• When generating staffusers, ALL users tied to the emails passed in staffusers.json are considered. Only the most recently active user is created into a StaffUser.
• When generating a UserPermission based on an email, if the email is tied to more than one user, the UserPermission is assigned to the most recently logged in user.

This PR also exposes Django admins to the User table with read-only access. This is so we can quickly identify duplicate users in our system without the need to perform an SSH operation.

How to test

1. Log into the local app to generate your user. Then, manually insert (or modify existing user emails) to create duplicate emails of your Login.gov email.
2. Make sure your email is in staffusers.json. Then, upon running the create_staffusers management command, ALL of the users with your email should have is_staffuser = true.
3. Confirm you exist as a StaffUser in Django admin.
4. Now that you have multiple users with the same email, try creating/editing/deleting a UserPermission with your email. You should encounter a successful response rather than an error.
5. Visit the Users table on Django admin and make sure it is a read-only table. Try sorting/searching, and clicking into users to make sure the correct content is displayed.

PR Checklist: Submitter

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Pre Merge Checklist: Merger

• Ensure that prior to approving, the terraform plan is what we expect it to be. -/+ resource "null_resource" "cors_header" should be destroying and recreating its self and ~ resource "cloudfoundry_app" "clamav_api" might be updating its sha256 for the fac-file-scanner and fac-av-${ENV} by default.
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[github-actions]

This pull request is not up to date with main. Please merge main into this brach or rebase this branch onto main. This PR should not be approved until all status checks pass. If you see this message, please rerun all status checks before merging.

[github-actions]

Terraform plan for meta

No changes. Your infrastructure matches the configuration.

No changes. Your infrastructure matches the configuration.

Terraform has compared your real infrastructure against your configuration
and found no differences, so no changes are needed.

📝 Plan generated in Pull Request Checks #4573

[github-actions]

Terraform plan for dev

Plan: 1 to add, 0 to change, 1 to destroy.

Terraform used the selected providers to generate the following execution
plan. Resource actions are indicated with the following symbols:
-/+ destroy and then create replacement

Terraform will perform the following actions:

  # module.dev.module.cors.null_resource.cors_header must be replaced
-/+ resource "null_resource" "cors_header" {
!~      id       = "*******************" -> (known after apply)
!~      triggers = { # forces replacement
!~          "always_run" = "2025-04-09T18:56:10Z" -> (known after apply)
        }
    }

Plan: 1 to add, 0 to change, 1 to destroy.

📝 Plan generated in Pull Request Checks #4573

[github-actions]

Package	Line Rate	Branch Rate	Health
.	100%	100%	✔
api	99%	87%	✔
api.serializers	97%	88%	✔
api.views	91%	100%	➖
audit	95%	80%	✔
audit.cross_validation	97%	85%	✔
audit.fixtures	84%	50%	❌
audit.intakelib	89%	83%	➖
audit.intakelib.checks	92%	85%	➖
audit.intakelib.common	98%	82%	✔
audit.intakelib.transforms	100%	95%	✔
audit.management.commands	78%	17%	❌
audit.migrations	100%	100%	✔
audit.models	92%	62%	➖
audit.templatetags	100%	100%	✔
audit.views	74%	55%	❌
census_historical_migration	96%	65%	✔
census_historical_migration.migrations	100%	100%	✔
census_historical_migration.sac_general_lib	92%	84%	➖
census_historical_migration.transforms	95%	90%	✔
census_historical_migration.workbooklib	68%	69%	❌
config	77%	37%	❌
curation	100%	100%	✔
curation.curationlib	93%	100%	➖
curation.migrations	100%	100%	✔
dissemination	91%	69%	➖
dissemination.migrations	97%	25%	✔
dissemination.report_generation	29%	0%	❌
dissemination.report_generation.excel	32%	0%	❌
dissemination.searchlib	59%	41%	❌
dissemination.templatetags	100%	100%	✔
dissemination.views	76%	55%	❌
djangooidc	53%	38%	❌
djangooidc.tests	100%	94%	✔
report_submission	100%	95%	✔
report_submission.migrations	100%	100%	✔
report_submission.templatetags	74%	100%	❌
report_submission.views	77%	63%	❌
support	93%	74%	➖
support.migrations	100%	100%	✔
support.models	90%	50%	➖
tools	98%	50%	✔
users	95%	86%	✔
users.fixtures	100%	83%	✔
users.management	100%	100%	✔
users.management.commands	100%	100%	✔
users.migrations	100%	100%	✔
Summary	89% (19942 / 22373)	71% (2429 / 3442)	➖

[jadudm]

LGTM. TY!