Add an option to disable showing bubbles EDU

Create a new debug setting to disable showing bubbles EDU. This can be
used in automated tests to ensure that showing EDU is more
deterministic. Most bubbles tests do not need to check for it and
specific EDU tests can be written to check it is shown correctly.

Bug: 294406308
Test: wipe the device and disable bubbles edu with the setting, open a
      bubble, check that edu does not show up
      reset the setting to hide edu, check that edu shows up next time a
      bubble is opened and that is shows only once
Change-Id: I514b096d687f54c65f314baef1d7508ffdd39627