Prioritize service response when showing issue type fetch error

What does this MR do and why?

service_response contains a more detailed error message that tells the user what they need to do to fix the problem.

This bug was discovered while trying to locally test the changes for !189200 (merged).

References

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Log in to GDK
2. Go to any project
3. Go to Settings -> Integrations and add a Jira Issues integration.
4. Check the box next to Create Jira issues for vulnerabilities
5. Enter any project key
6. Click the 🔄 button to try and fetch issue types
7. Receive detailed error message (before: would show "Validations failed.")

MR acceptance checklist

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