Add default open area settings

[zeroliu]

https://github.com/logancyang/obsidian-copilot/issues/749

• Refactored open window commands.
  • Deleted "toggle window in note area"
  • Added "open copilot chat window". Open command will reopen the chat view if one already exists. Toggle command will toggle the view.

• Added a setting to define the default open view: "editor" or "sidebar view".

[logancyang]

Wow this looks awesome!! 🎉