[examples] 新增trpc stream方式的文件上传简单示例

[yg66]

主要内容：

• 在examples目录下新增fileupload文件夹
• fileupload文件夹内包含：server、client、proto、ReadME.md
• 具体示例使用方式在ReadME.md中已经有提示
• 该示例主要针对trpc对于stream流形式的文件上传编写的简单demo，供大家参考

[github-actions]

Thank you for your submission, we really appreciate it. Like many open-source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution. You can sign the CLA by just posting a Pull Request Comment same as the below format.

---

I have read the CLA Document and I hereby sign the CLA

---

nil seems not to be a GitHub user. You need a GitHub account to be able to sign the CLA. If you have already a GitHub account, please add the email address used for this commit to your account.
_{You can retrigger this bot by commenting recheck in this Pull Request. Posted by the CLA Assistant Lite bot.}

[WineChord]

Suggested change

	module github.com/trpc-group/trpc-go/examples/features/stream/client
	module trpc.group/trpc-go/trpc-go/examples/features/fileupload/client

[WineChord]

README.md, not ReadME.md

[WineChord]

@yg66 Please sign CLA.