Allow migration of non-mirrored repositories as well

Is your feature request related to a problem? Please describe. I want to migrate a clone repository from another Git server, but I can only migrate a mirror repository, and when I try to migrate with mirror=false , an empty repository is created.

Describe the solution you'd like I want to be able to migrate even if mirror=false is specified as follows.

resource "gitea_repository" "clone" {
  username                     = "lerentis"
  name                         = "terraform-provider-gitea-clone"
  description                  = "Clone of Terraform Provider"
  mirror                       = false
  migration_clone_address      = "https://git.uploadfilter24.eu/lerentis/terraform-provider-gitea.git"
  migration_service            = "gitea"
  migration_service_auth_token = var.gitea_clone_token
}

Describe alternatives you've considered None

Additional context I will create a pull request for this issue.

Lerentis / terraform-provider-gitea

Allow migration of non-mirrored repositories as well #39