[ENH] improve the generation of the composer.json file at the root of tiki

• [ENH] improve the generation of the composer.json file at the root of tiki
• the composer.json file has composer.json.dist as a base to be generated. with the array merge method, in case of conflict when it finds the same key in both files it keeps the one coming from composer.json
• as the config is supposed to come from .dist I delete the one from composer.json in case of conflict.
• task