Add a way to set auth provider on rancher2_custom_user_token

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This is the tracking issue for #2108

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Description copied from PR:

Addresses #2102

Description

Add field auth_provider on resource rancher2_custom_user_token to generate token for ActiveDirectory user or others. If not set, default is local.
I change DoUserLogin function to use v3 API first, instead to continue to use v1. On my Rancher (2.13.1), the v1 api is still here, so it never use the new v3 API. It seems the v3 api support more auth provider like ping or custom_oidc.

Testing

I have compiled the binaire and put it on ~/.terraform.d/plugins/terraform.local/local/rancher2/0.1.1/linux_amd64/terraform-provider-rancher2.
You need to have Rancher with ActiveDirectory Auth provider setted (or other)

Then:

provider "rancher2" {
  api_url    = "https://rancher.local.domain"
  insecure   = true
  token_key      = "xxx"
}

resource "rancher2_custom_user_token" "test_ad" {
  auth_provider = "activedirectory"
  username = "user1"
  password = "xxx"
  description = "foo token"
  ttl = 0
}

To finish:

terraform apply

Not a breaking change.