Add new jsonb column to store settings for default branch protection

Currently, the options for default branch protection at the instance
and group level lag behind, and are not as fine-grained, as the
options available from the Protected Branches feature

The branch defaults lag behind because the current implementation uses
an integer column to store the default settings, which becomes
difficult to expand as new options and finer detail controls are added
to the protected branches feature

To offer better support of protected branches features on the default
branch, we can:

  1. use a jsonb column rather than an integer
  2. update the settings API to accept a payload the matches
     the protected branches API
  3. Pass those settings into the ProtecteBrancheService

This commit performs step 1, by adding a new `jsonb` column

Changelog: added