Added benchmark for Projects::CreateService

This benchmark currently runs at ~0.6 iterations per second and is
unlikely to perform any better any time soon.

spec/benchmarks/services/projects/create_service_spec.rb

+require 'spec_helper'
+
+describe Projects::CreateService, benchmark: true do
+  describe '#execute' do
+    let(:user) { create(:user, :admin) }
+
+    let(:group) do
+      group = create(:group)
+
+      create(:group_member, group: group, user: user)
+
+      group
+    end
+
+    benchmark_subject do
+      name    = SecureRandom.hex
+      service = described_class.new(user,
+                                    name:             name,
+                                    path:             name,
+                                    namespace_id:     group.id,
+                                    visibility_level: Gitlab::VisibilityLevel::PUBLIC)
+
+      service.execute
+    end
+
+    it { is_expected.to iterate_per_second(0.5) }
+  end
+end