feat(cloudreve): s3 policy support

[xrgzs]

支持上传到 Cloudreve S3 存储策略

[petercat-assistant]

Walkthrough: This PR introduces support for uploading to Cloudreve S3 storage by adding a new case for S3 in the policy type switch statement. It includes a new function upS3 to handle the upload process, and updates the UploadInfo struct to accommodate S3-specific fields.

Changes:

Files	Summary
drivers/cloudreve/driver.go	Added a new case for "s3" in the policy type switch statement to handle S3 uploads.
drivers/cloudreve/types.go	Updated UploadInfo struct to include CompleteURL for S3 uploads.
drivers/cloudreve/util.go	Implemented upS3 function to manage the S3 upload process, including multipart upload handling and completion.