Strip trailing spaces and tabs from every .md file in docs/, keeping indentation, and leave a .txt file alone.

Strip trailing spaces and tabs from every .md file in docs/, keeping indentation, and leave a .txt file alone.: a task in agent-harbor-tasks (Harbor dataset). togli gli spazi e le tabulazioni a fine riga da tutti i file .md in docs/. il resto non va toccato (nemmeno i file che non sono .md)