Time format should use time format setting added in 2021.6

[Unfocused]

Home Assistant 2021.6 added a time format setting per-user:

• https://www.home-assistant.io/blog/2021/06/02/release-20216/#time-format-settings
• Allow users to select time format for UI rendering home-assistant/frontend#9042

Available options are:

• Auto (use language setting) (DEFAULT)
• Use system locale
• 12 hours (AM/PM)
• 24 hours

Currently this card just uses the language setting, ignoring this user setting. Would be good if it followed the user preference.

AFAICT, it's available via hass.locale.time_format, which will be one of language, system, 12, or 24.