Merge branch 'docs-update-for-pipeline-validation' into 'master'

Document how results are presented from the pipeline validation service

See merge request gitlab-org/gitlab!61056

doc/administration/external_pipeline_validation.md

@@ -25,6 +25,10 @@ Response codes:
 - `4XX`: Not accepted
 - All other codes: accepted and logged
 
+### Service Result
+
+Pipelines not accepted by the external validation service aren't created or visible in pipeline lists, in either the GitLab user interface or API. Creating an unaccepted pipeline when using the GitLab user interface displays an error message that states: `Pipeline cannot be run. External validation failed`
+
 ## Configuration
 
 To configure external pipeline validation, add the