Document phone form field

[mjauvin]

related: wintercms/winter#1440

Summary by CodeRabbit

• Documentation
  • Added documentation for a Telephone (Tel) field: input rendering and HTML5 attributes, validation notes, datalist/autocomplete support, YAML configuration examples, preview/display behavior (phone icon, click-to-call), and guidance on option-label handling.
  • Updated the list of available field types to include Tel and URL.

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[mjauvin]

I made the changes.
To be fair, the URL field you created needs to be added to the field list as well... ;)