Calendar functionality

[realtmxi]

• add a calendar functionality, you can see at most three appointments in the calendar cell, and click more to see whole appointments, you can edit, delete appointment there

  • from the perspective of software engineering clean architecture principle, I never create a new calendar event entity as backend, I still insist using the design of appointment entity.

• achieve google calendar sync

  • you have to fulfill your GOOGLE_API_KEY and GOOGLE_CLIENT_ID under frontend/src/helpers/googleCalendarHelper.js to achieve the google calendar sync
  • Setup your environment: in the google cloud console, enable the google calendar API; configure the OAuth consent screen, then authorize credentials for a web application. To create an API key, go to Google Cloud console > APIs & Services > Credentials > APIkey > Restrict key