Function isFirstDayOfMonth

isFirstDayOfMonth(date?): boolean
Returns whether the given date is the first day of month
Parameters
- Optionaldate: Date
  the date to check
Returns boolean
whether the date is the first day of month
Example
```
isFirstDayOfMonth(new Date(2023, 8, 1));    // true
isFirstDayOfMonth(new Date(2023, 8, 30));    // false
```