feature request: Hide AJVs "unknown format" complaints

Describe the bug

According to the spec, format is is an open string-valued property, and can have any value. Spectral generates (pollutes?) stdout with warnings about "unknown format"s.

To Reproduce

repro/output.openapi.yaml

openapi: 3.0.0
servers:
  - url: "https://ex-ample.com"
x-format-version: "1.0"
info:
  title: Four
  description: Issue repro 4
  contact:
    email: [e-mail]
  version: 0.0.0
paths: {}
components:
  schemas:
    AModel:
      description: Yet another self descriptive explanation
      type: object
      properties:
        a_country:
          description: Guess what? A country.
          type: string
          format: "ISO-3166-1 alpha-2"
          example: de

Run

$ yarn spectral lint repro/output.openapi.yaml -o repro/log.txt -q
yarn run v1.15.2
$ C:\REDACTED\node_modules\.bin\spectral lint repro/output2.openapi.yaml -o repro/log.txt -q
unknown format "ISO-3166-1 alpha-2" ignored in schema at path "#"
unknown format "ISO-3166-1 alpha-2" ignored in schema at path "#"
Done in 1.52s.

repro/log.txt

(empty)

Expected behavior Nothing in stderr/stdout

Environment (remove any that are not applicable):

• Library version: 4.0.1
• OS: Windows 7

[philsturgeon]

Hey there, this related to https://github.com/epoberezkin/ajv/issues/466 in which the author of AJV makes it very clear that people should be aware of unknown formats.

I would like to try and hide these specific messages because you are correct, the OAS spec does say you can use whatever you want.

[chris-miaskowski]

and maybe a follow up feature could be to have those format messages converted to spectral warnings or info 😃

Sounds good. Had a quick look and surfacing it at the spectral messages level will require some more work.