CCM-11343: Prevent certain letter templates from being sync'd to core

[bhansell1]

Description

• adds a new field to LETTER templates called proofingEnabled. This field is calculated by checking if the template is RTL and if client configuration has proofing enabled
• a LETTER template created with proofingEnabled false will have a status of NOT_YET_SUBMITTED preventing the LETTER template requesting a proof
• adds publishing logic to the event-publisher lambda to exclude publishing LETTER template events that have proofingEnabled false & is not a publishable status. The filter will allow through all updates where templateType is not LETTER
• updates preview-letter-template page show to a callout when the LETTER language is classed as RTL

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

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