Allow setting multiple setting entries at once in settingStore

[huchenlei]

The current API only allows update single setting entry in a call (which correspond to an API call to update backend config json).

https://github.com/Comfy-Org/ComfyUI_frontend/blob/142882a8ff884e7c247acd3c1c10865ef91bf01c/src/stores/settingStore.ts#L70-L73

We should allow batch update of multiple setting entries in a single API call.