feat: ✨ set initial month in datepicker

[smfonseca]

User Story

As a user of the sd-datepicker, I want to set a specific month that the datepicker uses on initialization, so that the calendar opens on a predictable, relevant month (instead of always defaulting to the current month).

This should control the initially displayed month when the datepicker is first opened, it should not preselect a date, only define which month is shown first.

Suggested Solution

DoR

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DoD

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