feat: add sunday-start modifier

[itsmenewbie03]

This allows a cleaner way to make the calendar start on Sunday.

Currently to display make the calendar start on Sunday you have to do this

<x-mary-calendar locale="en-PH" :events="$events" weekend-highlight :config="['settings' => ['iso8601' => false]]" />

which IMO pretty verbose for a simple modification.

[robsontenorio]

Thanks!