CCM 9212 Fix styling on letter template

[nicki-nhs]

Description

• Adds missing spacing between form groups
• Adds missing padding on form groups
• Fixes missing font weight on form labels

Context

• The spacing between field sections on the page is not as per the design
• The field labels for 'Letter type' and 'Additional language' do not have the correct font weight to match the other field labels on the same page

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

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