Support OpenAPI and AsyncAPI validation cases

[jfallows]

Describe the desired outcome from the user's perspective
As an API consumer, I want to define OpenAPI validation behavior of zilla using the corresponding OpenAPI specification document for the HTTP API.

Acceptance criteria

• integer validation (text or binary)
  • int32, int64
  • max and min value
  • multiple of N
• number validation (text or binary)
  • float, double
  • max and min
  • multiple of N
• string validation
  • max and min length
  • regular expressions

Additional context
Review any remaining validation syntax in OpenAPI for enforcement via zilla model validation.