fix: strip aws-chunked when the request declares no payload type

`ParseContentEncoding` dropped the `aws-chunked` token only for streaming payload types, so a presigned request kept it: such a request is signed as `UNSIGNED-PAYLOAD` and sends no `x-amz-content-sha256` header, and S3 strips the token there. Keep it only when the request declares a non streaming payload type.

S3 applies this to the `Content-Encoding` header before any API sees it, so `CopyObject` and `CreateMultipartUpload` follow the same rule even though neither carries a body to frame. `POSTObject` takes its value from a form field rather than the header and is left alone.

s3api/controllers/object-post.go

@@ -147,7 +147,7 @@ func (c S3ApiController) CreateMultipartUpload(ctx fiber.Ctx) (*Response, error)
 	contentDisposition := ctx.Get("Content-Disposition")
 	contentLanguage := ctx.Get("Content-Language")
 	cacheControl := ctx.Get("Cache-Control")
-	contentEncoding := ctx.Get("Content-Encoding")
+	contentEncoding := utils.ParseContentEncoding(ctx)
 	tagging := ctx.Get("X-Amz-Tagging")
 	expires := ctx.Get("Expires")
 	websiteRedirectLocation := ctx.Get("X-Amz-Website-Redirect-Location")

s3api/controllers/object-put.go

@@ -516,7 +516,7 @@ func (c S3ApiController) CopyObject(ctx fiber.Ctx) (*Response, error) {
 	metaDirective := types.MetadataDirective(ctx.Get("X-Amz-Metadata-Directive", string(types.MetadataDirectiveCopy)))
 	taggingDirective := types.TaggingDirective(ctx.Get("X-Amz-Tagging-Directive", string(types.TaggingDirectiveCopy)))
 	contentType := ctx.Get("Content-Type", defaultContentType)
-	contentEncoding := ctx.Get("Content-Encoding")
+	contentEncoding := utils.ParseContentEncoding(ctx)
 	contentDisposition := ctx.Get("Content-Disposition")
 	contentLanguage := ctx.Get("Content-Language")
 	cacheControl := ctx.Get("Cache-Control")