Fixes #737: on_error support for Steps (Concourse)

headless-services/concourse-language-server/src/main/java/org/springframework/ide/vscode/concourse/PipelineYmlSchema.java

@@ -450,6 +450,7 @@ public class PipelineYmlSchema implements YamlSchema {
 			addProp(step, subStep, "on_success", step);
 			addProp(step, subStep, "on_failure", step);
 			addProp(step, subStep, "on_abort", step);
+			addProp(step, subStep, "on_error", step);
 			addProp(step, subStep, "ensure", step);
 			addProp(step, subStep, "tags", t_strings);
 			addProp(step, subStep, "timeout", t_duration);

headless-services/concourse-language-server/src/main/resources/desc/Step/on_error.md

@@ -0,0 +1,17 @@
+A hook step to execute after the parent step if the parent step terminates abnormally 
+in any way other than those handled by the [on_abort](https://concourse-ci.org/on-abort-hook.html#schema.on_abort) 
+or [on_failure](https://concourse-ci.org/on-failure-hook.html#schema.on_failure). 
+This covers scenarios as broad as configuration mistakes, temporary network issues with the workers, 
+or running longer than a timeout.
+
+##Example: Send a notification
+
+```
+plan:
+- do:
+  - get: ci
+  - task: unit
+    file: ci/unit.yml
+  on_error:
+    put: slack
+```