feat(spec): Add support for JSONPath and XPath where JSONPointer is supported

[frankkilcommins]

fixes: #366

Spec changes:

Expression Type Object

This replaces the previously named Criterion Expression Type Object and will be reused for both:

• Criterion Object
• Selector Object

Allowed type/version values remain:

Type	Allowed Versions	Default
jsonpath	rfc9535, draft-goessner-dispatch-jsonpath-00	rfc9535
xpath	xpath-31, xpath-30, xpath-20, xpath-10	xpath-31
jsonpointer	rfc6901 Just adding for completeness	rfc6901

Selector Object

Introduce a Selector Object, that can be used wherever more complex expressions than what's covered by the Arazzo ABNF grammer against structured data are required.

expression: string   # A valid Arazzo expression (e.g., $response.body)
selector: string     # A selector expression (e.g., $.items[0].id, /Envelope/Item)
type: string | Expression Type Object

Examples of usage:

outputs:
  userEmail:
    expression: $response.body
    selector: $.user.profile.email
    type: jsonpath

RequestBody example:

requestBody:
  contentType: application/json
  payload:
    invoiceId:
      expression: $steps.fetchXml.outputs.invoiceXml
      selector: /Invoice/Header/InvoiceNumber
      type:
        type: xpath
        version: 3.1

Places supporting {expression} for value setting have been extended to support the Selector Object.

Schema Updates

JSON Schema updated in line with spec changes

[kevinduffey]

LGTM.. I left one comment regarding regex.. there are 2 places that would apply I left it in just the one. If what is there is fine I'm good with that. Wasn't sure so thought I'd leave a "verify this is ok" comment. As such I'll 'request change' but feel free to ignore if its ok and then accept this as Approve.

[DmitryAnansky]

This might be a bit confusing for users. There will be two different ways to describe similar things.

There is already the context, but this PR also suggests expression. Maybe I misunderstood, but it seems to perform a similar role and set the context for the condition.
And selector is similar to condition, maybe without expressions.

              "context": "$response.body",
              "condition": "/Envelope/Status[text()='OK']",
              "type": {
                "type": "xpath",
                "version": "xpath-31"
              }

Were you considering reusing already described Criterion Object as Selector Object?