Add UNKNOWNS to Checkov reports

[AnthonyQ98]

Describe the feature

Checkov currently shows the results for PASSED, FAILED & SKIPPED checks. In some scenarios, policies can return UNKNOWN. In these scenarios, this evaluation (or lack of evaluation) is not included in the overall reports that Checkov produces.

This produces a gap in Checkov reporting. It can be important to know which Checks did not pass/fail, nor were they skipped, but instead could not return a determinisitic result. Measuring UNKNOWNS can be crucial to determine whether to keep a policy in place and accept the % of UNKNOWNS, or to remove it. This is currently not a supported behaviour by Checkov (UNKNOWNS are only visible in debug mode).

PR #7452 addresses this gap.

Examples

Before:

terraform_plan scan results:

Passed checks: 485, Failed checks: 55, Skipped checks: 0

New:

terraform_plan scan results:

Passed checks: 485, Failed checks: 55, Skipped checks: 0, Unknown checks: 132

JSON report:

Old:

"results": {
    "passed_checks": [...],
    "failed_checks": [...],
    "skipped_checks": [...]
  }

New:

"results": {
    "passed_checks": [...],
    "failed_checks": [...],
    "skipped_checks": [...],
    "unknown_checks": [
      {
        "check_id": "CKV_AWS_140",
        "check_name": "Ensure that RDS global clusters are encrypted",
        "resource": "module.db_module.module.global_cluster.aws_rds_global_cluster.global",
        "file_path": "/plan.json",
        "check_result": { "result": "UNKNOWN" }
      }
    ]
  }