Clarify pipeline's execution step and execution status

The enum values at https://github.com/AdobeDocs/cloudmanager-api-docs/blob/232bfdf117055fc2d9843b3fd970cdc50f2cf83e/swagger-specs/api.yaml#L1616 and https://github.com/AdobeDocs/cloudmanager-api-docs/blob/232bfdf117055fc2d9843b3fd970cdc50f2cf83e/swagger-specs/api.yaml#L1707 should be clarified with respect to differences between `error` and `failure`.

I assume that `failure` means the build failed due to some constraint violation while `error` is a transient error in the backend (so retries may work), but this is just my guess.

打开 swagger-specs/api.yaml 中 1616 行和 1707 行附近的 enum 定义。比较 pipeline execution-step 和 execution-status 的值，然后明确说明 `error` 和 `failure` 之间有文档记录的区别；当它们的含义和预期的重试行为都得到明确说明时，该 issue 即完成。

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