Reject duplicate resources with useful feedback

[textbook]

This is a:

• ✨ New feature - new behaviour has been implemented
• 🐛 Bug fix - existing behaviour has been made to behave
• ♻️ Refactor - the behaviour has not changed, just the implementation
• ✅ Test backfill - tests for existing behaviour were added but the behaviour itself hasn't changed
• ⚙️ Chore - maintenance task, behaviour and implementation haven't changed

Description

• Purpose - show useful feedback to the user when creation of their suggested resource fails

• How to check -

  • Log in as any user

  • Go to the suggestions page

  • Suggest a resource

    • A success message should appear and the form inputs should be cleared as previously:

      

  • Suggest another resource with the same name and/or URL

    • A message should appear telling the user the resource wasn't created, and the form input should not be cleared:

      

  • If the request fails 401, the user should still be logged out and sent back to the home page

  • If the request fails for any other reason, a more general error message is shown.

Links

Author checklist

• I have written a title that reflects the relevant ticket
• I have written a description that says what the PR does and how to validate it
• I have linked to the project board ticket (and any related PRs/issues) in the Links section
• I have added a link to this PR to the ticket
• I have made the PR to main from a branch named <category>/<name>, e.g. feature/edit-spaceships or bugfix/restore-oxygen
• I have manually tested that the app still works correctly
• I have requested reviewers here and in my team chat channel

• I have spoken with my PM or TL about any parts of this task that may have become out-of-scope, or any additional improvements that I now realise may benefit my project
• I have added tests, or new tests were not required
• I have updated any documentation (e.g. diagrams, schemas), or documentation updates were not required