DC-7892 / PIL-2496 - Add pillar2 template

[JamesMMiller]

Implements a HTML email template for Pillar 2 submission confirmations with conditional content for Below-Threshold Notification (BTN) requests.

Changes

• New service identifier: Added Pillar2 service identifier
• New template: pillar2_confirmation_email with conditional logic for BTN vs standard confirmations
• Template structure: Single template handles both scenarios using @if conditions based on requestType parameter

Template Behavior

• Default (non-BTN): Shows standard confirmation message with contact details
• BTN: Shows only BTN-specific content without default confirmation message
• ⚠️ Important: BTN detection requires exact string match: "Below Threshold Notification" (case-sensitive)

Required Parameters

Map(
  "confirmationDate"      -> "3 October 2025",        // Date of submission
  "confirmationTime"      -> "2:45pm",               // Time of submission  
  "requestType"           -> "UK Tax Return",         // One of: "UK Tax Return", "Below Threshold Notification", "Overseas Return Notification", "amended UK Tax Return", "amended Overseas Return Notification"
  "accountingPeriodStart" -> "1 April 2024",         // Start of accounting period
  "accountingPeriodEnd"   -> "31 March 2025"         // End of accounting period
)

BTN Request Type

Critical: For BTN-specific content to display, requestType must be exactly:

"Below Threshold Notification"

• Case-sensitive
• Exact string match required
• Any variation (e.g., "below threshold notification", "Below-Threshold Notification") will show default content instead

BTN Email:

Non-BTN email: