Allow for .yaml extension of appspec

According to this one:

https://stackoverflow.com/questions/21059124/is-it-yaml-or-yml/21059164

.yaml is the preferred extension to .yml

I think it does make sense that appspec could be appspec.yml AND appspec.yaml. A current codeDeploy task with appspec.yaml instead of appspec.yml fails with:

`The CodeDeploy agent did not find an AppSpec file within the unpacked revision directory at revision-relative path "appspec.yml". The revision was unpacked to directory
....
...
...`

The proper approach should be to allow for the deprecated .yml format but also to allow for .yaml file as that's the recommended extension.

首先检查 issue 中提到的 CodeDeploy 示例入口点和 AppSpec 文件名。确认必需的 appspec.yml 名称在哪里有文档说明或被强制要求，然后验证 appspec.yml 和 appspec.yaml 都能被接受，同时现有的 .yml 格式仍可继续工作。

由索引模型根据 Issue 内容生成。