Add Azure DevOps Server and Azure DevOps Services as valid OAuth client service providers

[lafentres]

Description

This adds support for using Azure DevOps Server and Azure DevOps Services as valid OAuth client service providers.

Depends on this go-tfe PR being merged first.

Also depends on this go-tfe PR being merged

Testing

1. Build the provider
2. cp $GOPATH/bin/terraform-provider-tfe ~/.terraform.d/plugins/
3. Use this config:

# Configure the Terraform Enterprise Provider
provider "tfe" {
  hostname = "NGROK"
  token    = "ADMIN_TOKEN"
}
resource "tfe_oauth_client" "ado_server" {
  organization     = "hashicorp"
  api_url          = "https://ado.hashicorp.engineering"
  http_url         = "https://ado.hashicorp.engineering"
  oauth_token      = "my-vcs-provider-token"
  service_provider = "ado_server"
}

resource "tfe_oauth_client" "ado_server_with_private_key" {
  organization     = "hashicorp"
  api_url          = "https://ado.hashicorp.engineering"
  http_url         = "https://ado.hashicorp.engineering"
  oauth_token      = "my-vcs-provider-token"
  service_provider = "ado_server"
  private_key      = "-----BEGIN RSA PRIVATE KEY-----\ncontent\n-----END RSA PRIVATE KEY-----"
}

resource "tfe_oauth_client" "ado_services" {
  organization     = "hashicorp"
  api_url          = "https://dev.azure.com"
  http_url         = "https://dev.azure.com"
  oauth_token      = "my-vcs-provider-token"
  service_provider = "ado_services"
}

4. Margaritas?

[svanharmelen]

LGTM!

[veverkap]

@svanharmelen @sudomateo asking for a rereview since we are now REQUIRING private_key for ado_server

[alisdair]

This looks good to me.

I think we could avoid ForceNew: true on the private key field with a little more work, but it's up to y'all whether you think that's worth it or not.

[svanharmelen]

I must admit I don't know Azure DevOps that well, but if this is required on their side I guess this makes sense. If it doesn't then I doubt if we should make it required...

As for the ordering, it's just my OCD kicking in trying to keep things consistent 😉

[lafentres]

This looks good to me! I left a couple of comments and I think it might be good to add a test case for the private key validation but that's it.