[CCM-13003] Prevent templates being deleted when part of a message plan

[nicki-nhs]

Description

• Checks whether routing configs reference given template ID when attempting to delete a template and prevents the action if so
• Creates new "Delete error" page which lists the routing configs referencing the template
• Updates lock number validation response to 400 from a 409

Context

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
• If I have used the 'skip-trivy-package' label I have done so responsibly and in the knowledge that this is being fixed as part of a separate ticket/PR.

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Sensitive Information Declaration

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• I confirm that neither PII/PID nor sensitive data are included in this PR and the codebase changes.