CCM-10177 custom personalisation fields to avoid list update and mino…

[emmagifford]

…r general improvements

Description

This PR includes the following changes to /using-nhs-notify/personalisation:

• updated the custom personalisation fields to avoid section in line with CCM-10177
• made general minor style improvements to other parts of the context

Context

See the ticket for the full context. We need to explicitly list all of the fields to avoid, and we need to clarify that punctuation variations will still cause the custom personalisation fields not to work.

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.

[jakecosgrove]

Nice work on making some of these more concise!