feat: add connect redirection + handle structure join

src/app/app-routing.module.ts

src/app/app.module.ts

src/app/form/form.component.html

src/app/form/form.component.scss

src/app/form/form.component.ts

src/app/guards/auth.guard.ts

src/app/header/header.component.ts

src/app/services/structure.service.ts

src/app/structure-join/structure-join.component.html

src/app/structure-join/structure-join.component.scss

src/app/structure-join/structure-join.component.spec.ts

src/app/structure-join/structure-join.component.ts

...onents/structure-details/structure-details.component.html

...mponents/structure-details/structure-details.component.ts