Disable the middle pages during development

Set isEnabled to false will prevent these middle pages which under
development get accidentally displayed to users.

During development, please flip isEnabled() of each page to true or
flip SpaEnvironment.IS_DEBUG to true to test these pages.

Bug: 244122804
Test: Manually with Settings
Change-Id: I5c3f835cfa3457b711d224ca37aa5d2b9a248feb