feat: Add a view for mentions (#3505)

- Added a new table mentions for saving user mentions
- Added a filter conversation_type in the API
- Added a view to see the mentions

db/schema.rb

@@ -531,6 +531,19 @@ ActiveRecord::Schema.define(version: 2021_12_08_085931) do
     t.index ["title", "account_id"], name: "index_labels_on_title_and_account_id", unique: true
   end
 
+  create_table "mentions", force: :cascade do |t|
+    t.bigint "user_id", null: false
+    t.bigint "conversation_id", null: false
+    t.bigint "account_id", null: false
+    t.datetime "mentioned_at", null: false
+    t.datetime "created_at", precision: 6, null: false
+    t.datetime "updated_at", precision: 6, null: false
+    t.index ["account_id"], name: "index_mentions_on_account_id"
+    t.index ["conversation_id"], name: "index_mentions_on_conversation_id"
+    t.index ["user_id", "conversation_id"], name: "index_mentions_on_user_id_and_conversation_id", unique: true
+    t.index ["user_id"], name: "index_mentions_on_user_id"
+  end
+
   create_table "messages", id: :serial, force: :cascade do |t|
     t.text "content"
     t.integer "account_id", null: false
@@ -764,6 +777,8 @@ ActiveRecord::Schema.define(version: 2021_12_08_085931) do
   add_foreign_key "csat_survey_responses", "messages"
   add_foreign_key "csat_survey_responses", "users", column: "assigned_agent_id"
   add_foreign_key "data_imports", "accounts"
+  add_foreign_key "mentions", "conversations"
+  add_foreign_key "mentions", "users"
   add_foreign_key "notes", "accounts"
   add_foreign_key "notes", "contacts"
   add_foreign_key "notes", "users"