Fix token issue

During the testing of the new indexer on staging, we've encountered a problem:

/opt/gitlab/embedded/service/gitlab-rails/ee/app/models/concerns/zoekt/searchable_repository.rb:68:in `use_new_indexer!': cannot find a default branch: rpc error: code = PermissionDenied desc = permission denied (RuntimeError)

The issue was that we forgot to pass the token to the client. This MR fixes this problem and adds a token to integration tests

Relates to gitlab#416935 (closed)