add library tag && library tag list api

app/controllers/library_tags_controller.rb

@@ -0,0 +1,6 @@
+class LibraryTagsController < ApplicationController
+  def index
+    library_tags = LibraryTag.all
+    render_ok(library_tags: library_tags.as_json(only: %i[id name]), count: library_tags.size)
+  end
+end

config/routes.rb

@@ -791,6 +791,7 @@ Rails.application.routes.draw do
     end
 
     resources :libraries, only: [:index, :show, :create, :update, :destroy]
+    resources :library_tags, only: [:index]
 
     scope module: :projects do
       resources :project_applies, only: [:create]

db/migrate/20190926024819_add_library_tag_data.rb

@@ -0,0 +1,9 @@
+class AddLibraryTagData < ActiveRecord::Migration[5.2]
+  def up
+    execute 'INSERT INTO library_tags(id, name) VALUES(4, "高校案例")'
+  end
+
+  def down
+    execute 'DELETE FROM library_tags WHERE id = 4 and name = "高校案例"'
+  end
+end