bug(secret): detect AWS secrets in image config

[DmitriyLewen]

Description

To avoid false positives when a random string contains part of an AWS secret, we look for a space character at the end of the secret.
But there are cases when there may be , after secret.
e.g. in image config (json format):

  {
  "created": "2023-11-30T23:11:03Z",
  "created_by": "ENV AWS_SECRET_ACCESS_KEY=wJalrXUtnFEMI/K7MDENG/bPxRfiCYEXAMPLEKEY",
  "comment": "buildkit.dockerfile.v0",
  "empty_layer": true
  },

Discussed in #5909