Setup pinning tests for boards

- Adds pinning script
- Adds pinning oracles

**How to create test oracle?**

```
PIN_TYPE=oracle scripts/pin_boards.sh
```

**How to run test?**

```
scripts/pin_boards.sh
```

ee/spec/features/boards/boards_pin_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe 'issue boards', :js do
+  include DragTo
+
+  let(:group) { create(:group, name: 'test_group') }
+  let(:owner) { create(:group_member, :owner, group: group, user: create(:user, name: 'shodan' )).user }
+  let(:project) { create(:project, :public, name: 'test_project', namespace: group) }
+  let(:board) { create(:board, project: project) }
+  let(:planning) { create(:label, project: project, name: 'Planning') }
+  let(:label) { create(:label, project: project) }
+  let(:milestone) { create(:milestone, project: project) }
+  let(:user) { create(:user) }
+
+  before do
+    stub_licensed_features(board_assignee_lists: true, board_milestone_lists: true)
+  end
+
+  shared_examples 'run pins' do |type|
+    let!(:list1) { create(:list, board: board, label: planning, position: 0) }
+    let!(:list2) { create(:list, board: board, label: label, position: 1) }
+    let!(:list3) { create(:milestone_list, board: board, milestone: milestone, position: 2) }
+    let!(:list4) { create(:user_list, board: board, user: owner, position: 3) }
+    let!(:issue) { create(:labeled_issue, project: project, title: 'abc', description: 'def', labels: [planning]) }
+    let!(:issue2) { create(:labeled_issue, project: project, title: 'hij', description: 'klm', labels: [label]) }
+    let!(:issue3) { create(:issue, project: project, title: 'nop', description: 'qrs', milestone: milestone) }
+
+    pin_type = ENV['PIN_TYPE'] || 'pin'
+    type = "#{type}.#{pin_type}"
+
+    it 'as_guest' do
+      project.add_guest(user)
+      login_as(user)
+
+      visit_board_page
+
+      save_pin('as_guest', type)
+    end
+
+    it 'as_developer' do
+      project.add_developer(user)
+      login_as(user)
+
+      visit_board_page
+
+      save_pin('as_developer', type)
+    end
+
+    it 'as_maintainer' do
+      project.add_maintainer(user)
+      login_as(user)
+
+      visit_board_page
+
+      save_pin('as_maintainer', type)
+    end
+  end
+
+  context "ff off" do
+    before do
+      stub_feature_flags(sfc_issue_boards: false)
+    end
+
+    it_behaves_like 'run pins', 'ff_off'
+  end
+
+  context "ff on" do
+    before do
+      stub_feature_flags(sfc_issue_boards: true)
+    end
+
+    it_behaves_like 'run pins', 'ff_on'
+  end
+
+  def visit_board_page
+    visit project_boards_path(project)
+    wait_for_requests
+  end
+
+  def save_pin(name, type)
+    path = File.dirname(__FILE__) + "/pins/#{name}.#{type}.html"
+
+    html = page.find('.boards-app')['outerHTML']
+
+    File.write(path, html, mode: 'wb')
+  end
+end

scripts/pin_boards.sh

+#!/usr/bin/env bash
+
+set -e
+
+PIN_TYPE="${PIN_TYPE:-pin}"
+SPEC_DIR="ee/spec/features/boards"
+SPEC_FILE="${SPEC_DIR}/boards_pin_spec.rb"
+PIN_DIR="${SPEC_DIR}/pins"
+
+echo "Running pins (${PIN_TYPE})..."
+
+bundle exec spring rspec "${SPEC_FILE}"
+
+for f in ${PIN_DIR}/*.${PIN_TYPE}.html; do
+  echo "Cleaning pin ($f)..."
+  sed -E -i.bak 's/127.0.0.1:[0-9]+/127.0.0.1/g; s/<!---->//g; s#assets/icons-[0-9a-zA-Z]+\.svg#assets/iconstest.svg#g' "$f"
+done
+
+rm ${PIN_DIR}/*.bak
+
+yarn run prettier --write "${PIN_DIR}/*.${PIN_TYPE}.html"
+
+if [ "$PIN_TYPE" = "pin" ]; then
+  for f in ${PIN_DIR}/*.${PIN_TYPE}.html; do
+    oracle=$(echo $f | sed 's/pin.html$/oracle.html/')
+    diff -u $oracle $f
+  done
+fi