First-class support for few-shot examples in front matter

[sternj]

Prerequisites

• I have checked the latest documentationand this feature doesn't exist
• I have searched for similar feature requests and found none
• I have linked to related issues or discussions in the description (if any exist)

Type of Improvement

New Functionality

Proposed Solution

Related to #140 , but a more specific proposal-- I think examples should live somewhere in the front matter.

The schemata of prompts can change quite a bit over time, and the current paradigm for few-shot examples in Prompty (just to use an additional block) doesn't do a make any effort to keep examples in lock-step with the input and output schemas, which I think it should be able to do.

The best solution I can see off the top of my head is a new top-level field, examples, that looks like the following (using the inputs and outputs blocks from this test

inputs:
  firstName:
    type: string
    default: User
    sample: April
    description: The first name of the customer
  lastName:
    type: string
    sample: Kwong
    required: true
    strict: false
    description: The last name of the customer
  question:
    type: string
    description: The question to answer
    required: true
outputs:
  work:
    type: object
    json_schema: ${file:schema.json}
    description: The thing to output
examples:
  - inputs:
      firstName: Ordinary
      lastName: Name
      question: Is this a realistic name?
    outputs:
      work:
        answer: It's not really my place to say
        items:
          - http://creative.url

Checking each of the examples is feasible given the information provided in the input and output specs. I know there might be other design constraints, so I wanted to make the suggestion and get some feedback before PRing the Python runtime