Update Pattern Registration flow in theme to use `patterns` directory

[fabiankaegy]

Description of the Change

WordPress 6.0 introduces the ability to register patterns via the patterns/ directory at the root of the theme. This mechanism makes it much simpler to manage patterns and therefore is what I would recommend going forward.

The Dev Note is not jet published but you can view the draft here: https://github.com/WordPress/gutenberg/issues/39654#issuecomment-1096823783

Closes #100

Alternate Designs

Possible Drawbacks

Verification Process

• Add a new PHP file in the patterns/ directory of the theme.
• Add the metadata comment at the top of the file and the block pattern markup underneath.

  
  <?php
  /**
  * Title: Example Pattern
  * Slug: tenup-theme/example
  * Categories: 10up-theme
  *
  * @package TenUpTheme
  */

?>

Example Pattern

- Open the editor and view that the pattern shows up in the pattern picker

### Checklist:

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- [ ] My change requires a change to the documentation.
- [x] I have updated the documentation accordingly.
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### Changelog Entry

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Changed how patterns are being registered to align with the API introduced in WordPress 6.0 

### Credits

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Props @