[Feature Request] Make chat input newline keybinding configurable (Shift+Enter support)

Bug Description
Feature request: Allow Shift+Enter to be a configurable keybinding for inserting a newline in the chat
input. Currently, Option+Enter (macOS) is hardcoded and cannot be rebound. Adding a chat:insertNewline
action to the keybindings system would allow users to customize this to Shift+Enter or other preferred
shortcuts.

Environment Info

• Platform: darwin
• Terminal: Apple_Terminal
• Version: 2.1.71
• Feedback ID: 8486432c-5ca9-4340-8a65-a3c35c361def

Errors

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