WS-592: Simple HTML CARTA wrapper for elegant expiration on countdown

• Modified carta_envoy to serve CARTA wrapped in a simple HTML countdown clock that dies elegantly to improve the UX when the timeout expires
• Unit tests
• Tested on dev
• Tested with AAT

added 15 commits

• a7f5f7ee...b4e1a464 - 14 commits from branch main
• 37d03a10 - Modified `carta_envoy` to serve CARTA wrapped in a simple HTML countdown

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added 1 commit

• 51c0d062 - Removed unused method left over from Janet's solution

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merged