Add option scrollOnKeypress

Note that we also change the existing behavior a bit:
CoreService.triggerDataEvent() will not scroll to the bottom unless
`wasUserInput` is also true. This actually seems to be the intended
behavior according to the doc just above
ICoreService.triggerDataEvent().

src/common/services/OptionsService.ts

@@ -28,6 +28,7 @@ export const DEFAULT_OPTIONS: Readonly<Required<ITerminalOptions>> = {
   linkHandler: null,
   logLevel: 'info',
   scrollback: 1000,
+  scrollOnKeypress: true,
   scrollSensitivity: 1,
   screenReaderMode: false,
   smoothScrollDuration: 0,