Enhancement: Field custom actions

[estruyf]

Allow custom actions to be linked to fields. This functionality works like custom actions/scripts, but it is triggered from a field.

Use case: allow users to create scripts to provide the field value. For example, use a script that calls your LLM to generate content.

Tasks

• Update the @frontmatter/extensibility dependency
• Integrate in the following field types:
  • Text field
  • Taxonomy field
  • Single image field
  • Multiple images field
• Documentation
  • Fields documentation
  • Extensibility documentation
• Schema generation + add scripts reference
• Examples