Handle Glip Webhook API Errors

[grokify]

When a 200 OK response handled, optionally allow client to return 400 status for better downstream handling:

{
  "status":"error",
  "message":"Your request was accepted, however a post was not generated",
  "error":"Invalid Custom payload",
  "validation":[
    "payload.attachments[0].fields[1] should have required property 'value'"
  ]
}