consider having sylva-units detect unit dependency loops

The following discussion from !2162 (closed) should be addressed:

• @feleouet started a discussion: (+1 comment)

  We are currently ignoring dependency loops in sylvactl, we should probably stop doing that to fail fast when such issues occurs. I've raised an issue for that: sylva-projects/sylva-elements/sylvactl#35 (closed)

  Maybe we could also follow-up on work done in !2054 (merged) and leverage/extend all-unit-dependencies template to detect dependency loops at templating level to fail even faster?