Implement brand image endpoints for APIv4 (#5733)

* Implement brand image endpoints for APIv4

* Fix unit test

api/admin.go

@@ -230,12 +230,6 @@ func getAnalytics(c *Context, w http.ResponseWriter, r *http.Request) {
 }
 
 func uploadBrandImage(c *Context, w http.ResponseWriter, r *http.Request) {
-	if len(utils.Cfg.FileSettings.DriverName) == 0 {
-		c.Err = model.NewLocAppError("uploadBrandImage", "api.admin.upload_brand_image.storage.app_error", nil, "")
-		c.Err.StatusCode = http.StatusNotImplemented
-		return
-	}
-
 	if r.ContentLength > *utils.Cfg.FileSettings.MaxFileSize {
 		c.Err = model.NewLocAppError("uploadBrandImage", "api.admin.upload_brand_image.too_large.app_error", nil, "")
 		c.Err.StatusCode = http.StatusRequestEntityTooLarge