Added a cover image

[MadeInShineA]

I added a default cover image (tempalte/cover_image_placeholder.png)

First I had to initialize the values inside the template/isc_template_report.typ file

The cover_image_height is set to 10 by default and the default caption is "Cover image caption"

cover_image: none,

cover_image_height: 10cm,

cover_image_caption: "Cover image caption",

Then I added a check to see if a cover image is set and create a figure accordingly

  if cover_image != none{
    figure(image(cover_image, height: cover_image_height), caption: cover_image_caption) 
  }

To position the image correctly, I had to add the following before the cover_image check

   v(10fr, weak: true)

To add the image, you have to add the wanted cover_image file name, cover_image_height and cover_image_caption to the project's variable inside the report.typ file

#show: project.with(
  title: "Rapport de projet ISC",
  course_name: "101.1 Programmation impérative",
  title_block: "Semestre automne 2023\nCours du Prof. P.-A. Mudry",
  cover_image: "cover_image_placeholder.png",
  cover_image_height: 10cm, // Default value = 10cm
  cover_image_caption: "Cover image caption", // Default value = "Cover image caption"
  sub_title: "Avec un joli sous-titre",
  authors: (
    "P.-A. Mudry",  
    "Louis Lettry",
    "Pamela Delgado"
  ),  
  logo: "isc_logo.svg",
  date: "5 décembre 2023",
  language: "fr", // Or en if required
  version: "1.0.0",
)  

The final result looks like this :

[pmudry]

Very nice feature and well written PR, thanks !