CCM-8354: NHS App test message details

[nicki-nhs]

Description

• Creates send-test-nhs-app-message page
• Creates SendTestMessage component which will be used for the other digital channels
• Creates TestPersonalisationForm and CustomFieldsForm components
• Refactors letter authoring to use the above components
• Adds util for NHS number validation
• Updates MarkdownContent to merge overrides on links
• Adds customPersonalisation and systemPersonalisation to schema for digital templates
• Extends functionality of template factory test helper
• Updates template repository to save custom and system personalisation to the DB when creating/updating templates

Context

Allows users to enter the details to request digital proofs of their NHS App templates

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.

[alexnuttall]

I think you need updates in update-template.api.spec.ts and create-template.api.spec.ts to cover the new field behaviours