[API] Handle multipart

[Yachef]

Example of generated code : Back (Java) :

@PostMapping(path = "", consumes = { "multipart/form-data" })
    void createFullCampagne(@RequestParam(value = "charte", required = false) MultipartFile charte, @ModelAttribute CampagneCreate campagne);

Front (Angular) :

createFullCampagne(campagne: CampagneCreate, charte: File): Observable<void> {
    const formData = new FormData();
    this.fillFormData(
        {
            ...campagne,
            charte
        },
        formData
    );
        return this.http.post<void>(`/campagnes`, formData);
}