implement Add Odometer Reading AppIntent

[OmarHegazy93]

What it Does

• Closes #222 Implement shortcut for adding new odometer reading

To achieve this task, I had to make some refactoring for the app flow by:

1. Removing the dependency for the AuthenticationViewModel for almost all viewModels, as they all needed the UserID only
2. UserID is currently saved to UserDefaults, as a next step we will need to figure out a better or safer way for saving it
3. Make getVehicles() method default implemented as both MainTabViewModel and SettingsViewModel are using it for fetching vehicles

For the AppIntent itself:

1. The query used to fetch the vehicles is using MainTabViewModel and if no vehicles available, then it will return an error
2. DistanceUnit enum is used to make more readable for selecting Distance unit
3. Validation is applied to Distance and Date

How I Tested

Happy scenario

1. Install the app
2. Make sure at least one vehicle is added in the app by going to Settings tab > Add Vehicle
3. Switch to Shortcuts app
4. Tab on the + on the top right corner
5. Tab on ⨁ Add Action
6. Select Apps tab
7. Tab on Basic Car
8. Tab on Add Odometer Reading
9. Add data for all fields and tab the play button on the bottom right corner
10. See the result

Unhappy scenario

1. Install the app
2. Make sure at least one vehicle is added in the app by going to Settings tab > Add Vehicle
3. Switch to Shortcuts app
4. Tab on the + on the top right corner
5. Tab on ⨁ Add Action
6. Select Apps tab
7. Tab on Basic Car
8. Tab on Add Odometer Reading
9. Try to set distance value to zero or negative value or set the date to past
10. See the result

Notes

• Anything else that should be noted about how you implemented this feature?

Screenshot

• Add a screenshot of your new feature! OR show a screen recording of it in action. (On the simulator press Cmd + R to record, and the stop button when done). This video should be no longer than 30 seconds.

[mikaelacaron]

Closing now that Hacktoberfest is over, and I don't want to merge this solution right now. Thanks again for contributing! It's much appreciated! Feel free to pick up any issues even though Hacktoberfest is over