Support Custom GitHub Action authoring

**Is your feature request related to a problem? Please describe.**
As a developer of some GitHub Actions, I would like to have the same level of help on the `action.yaml` (or `.yml` file), especially for composite actions.

**Describe the solution you'd like**
Detect the action file and setup schema validation and the same behavior of the `Workflow authoring` feature adapt to it.

**Additional context**

Add syntax highlighting on input for example, and so on

首先检查现有的 Workflow 编写功能，以及如何检测 action.yaml 或 action.yml 文件。当自定义 action，尤其是 composite action，获得等效的 schema 验证和编写辅助功能（包括输入语法高亮）时，这项工作就完成了。

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