Add OAuth2 authentication (#147)

- Added Site settings > Authentication section
- Create/edit/delete your custom oauth2 configurations
- Login or signup with oauth2

db/migrate/20220727090932_create_o_auths.rb

@@ -0,0 +1,22 @@
+class CreateOAuths < ActiveRecord::Migration[6.0]
+  def change
+    create_table :o_auths do |t|
+      t.string :name, null: false
+      t.string :logo
+      t.boolean :is_enabled, default: false
+      t.string :client_id, null: false
+      t.string :client_secret, null: false
+      t.string :authorize_url, null: false
+      t.string :token_url, null: false
+      t.string :profile_url, null: false
+      t.string :scope, null: false
+      t.string :json_user_name_path
+      t.string :json_user_email_path, null: false
+      t.references :tenant, null: false, foreign_key: true
+
+      t.timestamps
+    end
+
+    add_index :o_auths, [:name, :tenant_id], unique: true
+  end
+end