Improve admin for source systems

[hmpf]

Scope and purpose

A bug in create_source necessitated using the admin to create a source and that was also fraught with peril.

This PR is a collection of admin changes to make working with sources easier.

Screenshots

User admin, before:

User admin, after:

Contributor Checklist

Every pull request should have this checklist filled out, no matter how small it is.
More information about contributing to Argus can be found in the
Development docs.

• Added a changelog fragment for towncrier
• Added/amended tests for new/changed code
• Added/changed documentation, including updates to the user manual if feature flow or UI is considerably changed
• Linted/formatted the code with ruff and djLint, easiest by using pre-commit
• The first line of the commit message continues the sentence "If applied, this commit will ...", starts with a capital letter, does not end with punctuation and is 50 characters or less long. See our how-to
• If applicable: Created new issues if this PR does not fix the issue completely/there is further work to be done
• If this results in changes in the UI: Added screenshots of the before and after
• If this results in changes to the database model: Updated the ER diagram

[sonarqubecloud]

Quality Gate failed

Failed conditions
C Reliability Rating on New Code (required ≥ A)

See analysis details on SonarQube Cloud

Catch issues before they fail your Quality Gate with our IDE extension SonarQube for IDE

[github-actions]

Test results

    6 files    810 suites   1m 38s ⏱️
  638 tests   637 ✅ 1 💤 0 ❌
3 828 runs  3 822 ✅ 6 💤 0 ❌

Results for commit 3d6377f.

♻️ This comment has been updated with latest results.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.22%. Comparing base (91decd0) to head (3d6377f).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1660   +/-   ##
=======================================
  Coverage   80.22%   80.22%           
=======================================
  Files         133      133           
  Lines        6271     6271           
=======================================
  Hits         5031     5031           
  Misses       1240     1240           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[sonarqubecloud]

Quality Gate failed

Failed conditions
C Reliability Rating on New Code (required ≥ A)

See analysis details on SonarQube Cloud

Catch issues before they fail your Quality Gate with our IDE extension SonarQube for IDE