substreams init default project name should be derived from folder name

[maoueh]

Right now, substreams init generates file in the current directly. It's likely that the folder's name is the Substreams project's name.

Instead of hardcoding my_project, use something like strings.ReplaceAll(sanitizeProjectNameFromParentFolder(filepath.Base(filepath.Dir(os.Getcwd()))), "-", "_") .