Add index endpoint request spec
user
```ruby
require 'rails_helper'

describe "GET /districts/:district/endpoints", type: :request do
  let(:user) { create :user }
  let(:district) { create :district }

  it "returns a list of endpoint" do
    district.endpoints.create(name: "ep1")
    district.endpoints.create(name: "ep2")

    api_request(:get, "/v1/districts/#{district.name}/endpoints")
    expect(response.status).to eq 200
    endpoints = JSON.load(response.body)["endpoints"]
    expect(endpoints.count).to eq 2
    expect(endpoints[0]["name"]).to eq "ep1"
    expect(endpoints[0]["dns_name"]).to be_blank
    expect(endpoints[1]["name"]).to eq "ep2"
    expect(endpoints[1]["dns_name"]).to be_blank
  end
end
```
assistant