Use app-page-header component in signup page + update style of the page

src/app/user/components/auth/sign-up/sign-up.component.html

src/app/user/components/auth/sign-up/sign-up.component.scss

src/app/user/components/auth/sign-up/sign-up.component.ts

src/app/user/user.module.ts

src/i18n/messages.en.xlf

src/i18n/messages.fr.xlf

src/i18n/traductions.fr.ts

src/i18n/traductions.ts

src/styles.scss