Implement file type creation endpoint

Completed the `newType` method in `files.controller.ts` to call `filesService.createFileType` with the provided name and mime type. This enables the creation of new file types through the backend API.

apps/backend/src/app/files/files.controller.ts

@@ -143,7 +143,7 @@ export class FilesController {
 	@UseGuards(AdminGuard)
 	@Post("types/new")
 	async newType(@Body() body: CreateFileTypeDto) {
-		//TODO
+		return await this.filesService.createFileType(body.name, body.mime)
 	}
 
 	@HttpCode(HttpStatus.ACCEPTED)