fix: vulnerability scans of unsupported images

Lacework runs vulnerability scans only against the following list of
supported distributions:

* https://support.lacework.com/hc/en-us/articles/360035472393-Container-Vulnerability-Assessment-Overview

Any other container image that is not listed there is unsupported and we
will be displaying an error message similar to:
```
$ lacework vul report sha256:04e8df550c7b52cd8ec64143a1c853cd76b234b29ad9e37149ffe04786acd142
Usage:
  lacework vulnerability report <sha256:hash> [flags]

Flags:
      --details    increase details about the vulnerability report
      --digest     tread the provided sha256 hash as image digest (DEPRECATED) (default true)
  -h, --help       help for report
      --image_id   tread the provided sha256 hash as image id

Global Flags:
  -a, --account string      account subdomain of URL (i.e. <ACCOUNT>.lacework.net)
  -k, --api_key string      access key id
  -s, --api_secret string   secret access key
      --debug               turn on debug logging
      --json                switch commands output from human-readable to json format
      --nocolor             turn off colors
      --noninteractive      disable interactive progress bars (i.e. 'spinners')
  -p, --profile string      switch between profiles configured at ~/.lacework.toml

ERROR unable to get report for the provided container image. (unsupported distribution)

For more information about supported distributions, visit:
    https://support.lacework.com/hc/en-us/articles/360035472393-Container-Vulnerability-Assessment-Overview
```

Closes #132

Signed-off-by: Salim Afiune Maya <[email protected]>

cli/cmd/vulnerability.go

@@ -243,6 +243,14 @@ lookup a report by its image id, provided the flag '--image_id'.
 				}
 
 				cli.OutputHuman(buildVulnerabilityReport(&report.Data))
+			case "Unsupported":
+				return errors.Errorf(
+					`unable to retrieve report for the provided container image. (unsupported distribution)
+
+For more information about supported distributions, visit:
+    https://support.lacework.com/hc/en-us/articles/360035472393-Container-Vulnerability-Assessment-Overview
+`,
+				)
 			case "NotFound":
 				msg := fmt.Sprintf(
 					"unable to find any container vulnerability report with %s '%s'",
@@ -362,6 +370,14 @@ func checkScanStatus(requestID string, lacework *api.Client) (*api.VulContainerR
 		return &scan.Data, nil, false
 	case "Scanning":
 		return &scan.Data, nil, true
+	case "Unsupported":
+		return nil, errors.Errorf(
+			`unable to run assessment for the provided container image. (unsupported distribution)
+
+For more information about supported distributions, visit:
+    https://support.lacework.com/hc/en-us/articles/360035472393-Container-Vulnerability-Assessment-Overview
+`,
+		), false
 	case "NotFound":
 		return nil, errors.Errorf(
 			"unable to find any vulnerability scan with request id '%s'",