fix: gracefully handle DoesNotExist exceptions for tokens

[rohan-chaturvedi]

🔍 Overview

When the REST api is accessed with a deleted token, it incorrectly errors out with a status 500 code. This due to the token's DoesNotExist exception not being handled correctly during the intial token validation check

💡 Proposed Changes

Gracefully hande DoesNotExist errors and return status 403 response

📝 Release Notes

Fix a bug with REST api authentication when using deleted tokens

💚 Did You...

• Ensure linting passes (code style checks)?
  - [ ] Update dependencies and lockfiles (if required)
  - [ ] Regenerate graphql schema and types (if required)
• Verify the app builds locally?
• Manually test the changes on different browsers/devices?