text: Title: Confusing error
  Body: Ploomber fails with a confusing error when trying to build a pipeline and there is no pipeline.yaml (also happens implicitly because this is the default value). since it can’t find the file, the next thing it tries is to import a “pipeline” module
  
  Pipeline.yaml is an special case that should be covered but for any cases where a file could be interpreted as a dotted path maybe just show a clearer error message: “failed to load entry point ‘file.ext’, file does not exist and there is no module called ‘file’ either”