Two components of the boundary of \(\text \textbf{I}_3\). (Deux composantes du bord de \(\text \textbf{I}_3\)) On the embedding of \(\text{Gal}(\overline\mathbb{Q}/\mathbb{Q})\) into \(\widehat{GT}\). (Appendix by Michel Emsalem and Pierre Lochak: The action of the absolute Galois group on the moduli space of spheres with four marked points) 