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

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