Syntax highlighting for repos that put composite workflows in directories other than `.github`

**Is your feature request related to a problem? Please describe.**
It's often nice to put shared workflows in directories that make sense for consumers, like `my-private-org/composite/some-team-name/their-reusable-workflow.yml`. The extension works fine for _resolving_ these workflows when they're used, but it doesn't syntax highlight or do anything when _authoring_ these workflows. It seems to pay attention to `.github/**/*.yml` exclusively.

**Describe the solution you'd like**
Configurable paths and options for which files should be parsed.

**Additional context**
Add any other context or screenshots about the feature request here.

首先追踪扩展在编写工作流时仅解析 `.github/**/*.yml` 的逻辑，并确定负责语法高亮和文件发现的入口点。定义应如何提供可配置路径和解析选项，然后验证位于 `composite/some-team-name/` 等目录中的工作流也能获得相同的编写支持。

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