docs(datepicker): fix config example

[bastienmoulia]

Fix #3848 and #3873 but maybe the documentation is OK and it's the NgbInputDatepickerConfig which do not works well.

[maxokorokov]

I don't think the issue is with the demo. I don't think it should work this way, there should be only NgbInputDatepickerConfig.

• input config extends normal config, so it has all the same stuff
• we provide it here →

  ng-bootstrap/src/datepicker/datepicker-input.ts

  Line 65 in 0ee1966

  { provide: NgbDatepickerConfig, useExisting: NgbInputDatepickerConfig },

• only inputdatepikcer-specific inputs are initalized for some reason →

  ng-bootstrap/src/datepicker/datepicker-input.ts

  Line 104 in 0ee1966

  @Input() autoClose = this._config.autoClose;

  these are not →

  ng-bootstrap/src/datepicker/datepicker-input.ts

  Line 176 in 0ee1966

  @Input() minDate: NgbDateStruct;

• when we open datepicker popup, we copy inputs here →

  ng-bootstrap/src/datepicker/datepicker-input.ts

  Lines 532 to 554 in 0ee1966

  	private _applyDatepickerInputs(datepickerComponentRef: ComponentRef<NgbDatepicker>): void {
  	[
  	'contentTemplate',
  	'dayTemplate',
  	'dayTemplateData',
  	'displayMonths',
  	'firstDayOfWeek',
  	'footerTemplate',
  	'markDisabled',
  	'minDate',
  	'maxDate',
  	'navigation',
  	'outsideDays',
  	'showNavigation',
  	'showWeekNumbers',
  	'weekdays',
  	].forEach((inputName: string) => {
  	if (this[inputName] !== undefined) {
  	datepickerComponentRef.setInput(inputName, this[inputName]);
  	}
  	});
  	datepickerComponentRef.setInput('startDate', this.startDate || this._model);
  	}

It all doesn't seem right... input config should NOT extend the normal one, if you have to inject both.

Maybe we just need to initialize ALL inputs with the config values? but then what's the reason for providing NgbDatepickerConfig... I can't see what's broken, need to write tests..