[TEP-0050] Add Ignore Task Failure to alpha table

This commit adds "Ignore Task Failure" to the alpha feature table.

/kind documentation

docs/additional-configs.md

@@ -319,6 +319,7 @@ Features currently in "alpha" are:
 | [CEL in WhenExpression](./taskruns.md#cancelling-a-taskrun)                    | [TEP-0145](https://github.com/tektoncd/community/blob/main/teps/0145-cel-in-whenexpression.md)                       | [v0.53.0](https://github.com/tektoncd/pipeline/releases/tag/v0.53.0) | `enable-cel-in-whenexpression`                   |
 | [Param Enum](./taskruns.md#parameter-enums)                                    | [TEP-0144](https://github.com/tektoncd/community/blob/main/teps/0144-param-enum.md)                                  | [v0.54.0](https://github.com/tektoncd/pipeline/releases/tag/v0.54.0) | `enable-param-enum`                              |
 | [Reusable Steps via StepActions](./stepactions.md)                             | [TEP-0142](https://github.com/tektoncd/community/blob/main/teps/0142-enable-step-reusability.md)                     | [v0.54.0](https://github.com/tektoncd/pipeline/releases/tag/v0.54.0) | `enable-step-actions`                            |
+| [Ignore Task Failure](./pipelines.md#using-the-onerror-field)                             | [TEP-0050](https://github.com/tektoncd/community/blob/main/teps/0050-ignore-task-failures.md)                     | N/A |                            |
 
 ### Beta Features