CCM-12274: Rework NHSApp callback design diagrams

[tdroza-nhs]

Description

Diagram updates:

• Renamed the NHSAppCallbackHandler component to NHSApp Status Handler
• Changed design from consuming an webhook callback from Core, to receiving an event via the shared event bus
• Removed the sequence diagram as the flow is now the same as all other components

Context

Enables receipt of the PrintLetterOptedOut status from NHSApp to suppress sending the PDF for print

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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Sensitive Information Declaration

To ensure the utmost confidentiality and protect your and others privacy, we kindly ask you to NOT including PII (Personal Identifiable Information) / PID (Personal Identifiable Data) or any other sensitive data in this PR (Pull Request) and the codebase changes. We will remove any PR that do contain any sensitive information. We really appreciate your cooperation in this matter.

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