fix: create exception returning the wrong HTTP code

[will-larkin-nhs]

Description

• changed create exception to return OK instead of CREATED

Context

In a previous PR, create exception was changed to return CREATED to fix a sonarqube issue, but the exception handler client expects an OK response, so this was causing the create exception request to be logged as a failure

Type of changes

• Refactoring (non-breaking change)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would change existing functionality)
• Bug fix (non-breaking change which fixes an issue)

Checklist

• I am familiar with the contributing guidelines
• I have followed the code style of the project
• I have added tests to cover my changes
• I have updated the documentation accordingly
• This PR is a result of pair or mob programming

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