feat(GlDateRangePicker): Add daterange indicator and help icon

What does this MR do?

Adds a optional default slot to display the selected date range and help icon with a tooltip.

Related to gitlab#335357 (closed).

Design issue gitlab-org/gitlab-services/design.gitlab.com!2438 (merged):

When the date range has a limit on the number of selectable days, indicate that in the UI with text summarizing the number of days currently selected, and an info icon specifying the date range limit.

Screenshots

before	after

Does this MR meet the acceptance criteria?

Conformity

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• Added the ~"component:*" label(s) if applicable.

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Accessibility

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• All actions and functionality can be done with a keyboard.
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