Input Blob Binding name fails with an activity trigger

🐛 **Describe the bug**
Input Blob Binding name fails with an activity trigger

🤔 **Expected behavior**
activity function takes a string argument (the name of a blob) and uses that value to bind to blob input

☕ **Steps to reproduce**

try to bind a blob name to the value passed in an activity trigger

{
"scriptFile": "__init__.py",
"bindings": [
{
"name": "name",
"type": "activityTrigger",
"direction": "in"
},
{
"name": "inputb",
"direction": "in",
"type": "blob",
"path": "container/{name}.json",
"connection": "AzureWebJobsStorage",
"dataType": "string"
}
]
}

Should work like explained in this link but fails in Pyhon
https://github.com/Azure/azure-functions-durable-extension/pull/172

首先，使用 __init__.py 作为脚本入口点，复现 issue 中所示的 activity trigger 和 blob binding 配置。将 Python 的行为与所引用的 durable-extension PR 进行比较，并跟踪 activity 参数如何传入 blob 路径。当根据 activity 参数命名的 blob 成功绑定为输入时，即表示完成。

由索引模型根据 Issue 内容生成。