[GITEA] Fix API inconsistencies

- Document the correct content types for Git archives. Add code that
actually sets the correct application type for `.zip` and `.tar.gz`.
- When an action (POST/PUT/DELETE method) was successful, an 204 status
code should be returned instead of status code 200.
- Add and adjust integration testing.
- Resolves #2180
- Resolves #2181

(cherry picked from commit 6c8c4512b530e966557a5584efbbb757638b3429)
(cherry picked from commit 3f74bcb14df99ee75a170813979beb5ce04c8027)
(cherry picked from commit 6ed9057fd76b2d5d0dfdb3c663367ae861ab8093)

routers/api/v1/repo/file.go

@@ -257,7 +257,9 @@ func GetArchive(ctx *context.APIContext) {
 	// ---
 	// summary: Get an archive of a repository
 	// produces:
-	// - application/json
+	// - application/octet-stream
+	// - application/zip
+	// - application/gzip
 	// parameters:
 	// - name: owner
 	//   in: path
@@ -337,7 +339,17 @@ func download(ctx *context.APIContext, archiveName string, archiver *repo_model.
 	}
 	defer fr.Close()
 
+	contentType := ""
+	switch archiver.Type {
+	case git.ZIP:
+		contentType = "application/zip"
+	case git.TARGZ:
+		// Per RFC6713.
+		contentType = "application/gzip"
+	}
+
 	ctx.ServeContent(fr, &context.ServeHeaderOptions{
+		ContentType:  contentType,
 		Filename:     downloadName,
 		LastModified: archiver.CreatedUnix.AsLocalTime(),
 	})