Component nav: reworked and pattern nav_item removed

• use links prop type for menu elements: improve site building features
• add card_header prop type to remove the last pattern preprocess
• add tab_content slot for easier tab content generation (maybe not site buildable, but at least it ease custom development)

Nav component changes:

• The items slot has been converted into a links type prop to improve site building and consistency for navigation handling.
• A card_header prop had been added to be able to remove the last pattern preprocess and prepare for UI Patterns 2.
• A nav_id prop had been added for cases where a nav ID is needed, like https://getbootstrap.com/docs/5.3/components/navs-tabs/#javascript-behavior
• A tab_content has been added to ease the usage of https://getbootstrap.com/docs/5.3/components/navs-tabs/#javascript-behavior, maybe not site buildable, but it eases the custom developments.

As the nav_item component was only intended to be used in the nav component and initially structured before the introduction of the links prop type, it is now obsolete and it has been removed.