Use storage_endpoint from config when creating artifacts

[kochkarev]

Overview of the Issue

Variable defaultStorageEndpoint is used to create artifacts of yandex-export, while it can be set in config.
https://github.com/hashicorp/packer-plugin-yandex/blob/b9733757549440a34dc958598c8f7e4cecb5c015/post-processor/yandex-export/post-processor.go#L387C47-L387C47

Reproduction Steps

1. Set storage_endpoint in post-processor "yandex-export"
2. You will get "artifact_id": "https://storage.yandexcloud.net/ always in build artifacts

Plugin and Packer version

yandex-export

Simplified Packer Buildfile

post-processor "yandex-export" {
      endpoint           = "my-custom-endpoint"
      storage_endpoint   = "my-custom-storage-endpoint"

      folder_id          = var.folder_id
      service_account_id = var.service_account_id
      subnet_id          = var.subnet_id
      zone               = var.zone

      use_ipv6 = true

      platform_id  = "standard-v3"

      paths = [
        "${var.s3_path}/${source.name}-{{build `ImageID`}}",
      ]
      keep_input_artifact = true
}

Operating system and Environment details

any