Replace native date input field with `GlDatePicker`

What does this MR do and why?

In Profile > SSH keys, I replaced the native date field with the ExpiresAtField Vue component (which uses GlDatePicker). ExpiresAtField renders by default a date of 30 days in the future. That was an security recommendation for access tokens (see !93128 (merged)), but I am unsure if that would be beneficial also in the SSH context.

Because ExpiresAtField doesn't horizontally align with the title field I decided to move to the next row.

Closes #271239 (closed)

Screenshots or screen recordings

Before

After

How to set up and validate locally

The new datepicker is in this page: https://gdk.test:3443/-/profile/keys

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