Document multiple selection option for Select ingredient

[antwertinger]

Summary

Adds documentation for the new multiple setting on the Select ingredient that enables multiple value selection.

Changes

• Updated Select ingredient description to explain Array storage for multiple selections
• Added multiple: true setting documentation with default value
• Added two examples: single selection (default) and multiple selection
• Clarified that values are stored as String by default and as Array when multiple is enabled

Example Usage

- name: categories
  type: Select
  settings:
    select_values: ['Technology', 'Design', 'Marketing', 'Sales']
    multiple: true