Allow include to be specified in .gitlab-ci.yml

The following can be added to .sync.yml to specify an include block

.gitlab-ci.yml:
   include:
     - local: /.gitlab-ci-local.yml'
     - project: my-group/my-project'
       file: /.gitlab-ci-another-project.yml'

• https://docs.gitlab.com/ee/ci/yaml/#include