[Task] add upload file example and integrated test

[loongs-zhang]

Description

Currently, although ShenYu supports the upload interface of forwarding files, there are no relevant examples and integration tests. This task needs you to finish these.

The upload file can be committed to shenyu-examples/shenyu-examples-common/src/main/resources, just upload one file.

During integration testing, ~~you may need to unzip the fat jar of SpringBoot~~.

just create and write new file, check https://github.com/apache/shenyu/pull/3768

Task List

1. • [x] add file upload example for shenyu-examples-http; @847850277
2. • [ ] add file upload example for shenyu-examples-https; @lahmXu
3. • [x] add file upload example for shenyu-examples-springmvc; @847850277
4. • [x] add file upload example for shenyu-examples-springmvc-tomcat; @847850277
5. • [ ] add file upload example for shenyu-examples-websocket; @mahaitao617
6. • [x] add file upload integration test for shenyu-integrated-test-http; @847850277
7. • [ ] add file upload integration test for shenyu-integrated-test-https; @lahmXu
8. • [ ] add file upload integration test for shenyu-integrated-test-spring-cloud; @lahmXu
9. • [ ] add file upload integration test for shenyu-integrated-test-websocket; @mahaitao617
10. • [ ] add file upload example for shenyu-examples-springcloud; @lahmXu

[mahaitao617]

please assign task5 and task9 to me

[847850277]

please assign task 1、3、4、6 to me.

[lahmXu]

Please assign task 2,7,8,10 to me, thanks!

[loongs-zhang]

Thanks for your contribution !