feat(vscode): reorganize settings

[wwayne]

Main changes

Update the settings page

trigger mode in settings.json

New context variable tabby.inlineCompletionTriggerMode

After putting inlineCompletionTriggerMode into settings.advanced, we can't visit config.tabby.settings.advanced.inlineCompletion.triggerMode
So I create a new context variable

Trigger mode testing

• Command palette (toggle command)
• Bottom-right popup for different trigger mode
• Manually updating the settings.json