Add wildcard/calendar component based on 'react-calendar' npm package

Created by: erzhtor

Part 1 of https://github.com/sourcegraph/sourcegraph/issues/40593.

For the new user-management page, we need to add column filters, and some columns are of date type. This PR adds a Calendar component based on react-calendar, with basic Sourcegraph styles (light/dark mode) that supports date or date range selection.

Note: there are not many existing react library options that would be simple and yet allow us fully style it.

@sourcegraph/frontend-platform, @rrhyne I thought that this base Calendar could be useful to extract into wildcard in case there will be some other places where a calendar or date range picker will be needed. However, if you think this should not be included in the wildcard yet, I can close this PR and just include it directly in the user-management page folder.

Test plan

• yarn storybook:wildcard
• Open http://localhost:9001/?path=/story/wildcard-calendar--mode-range

Screenshots

Description	screenshot
single date select mode
	<Calendar value={value as [Date, Date]} onChange={onChange} />
date range select mode
	<Calendar mode="range" value={value as [Date, Date]} onChange={onChange} />
dark mode

App preview:

• Web
• Storybook

Check out the client app preview documentation to learn more.