front: collapse scenario description

If the scenario description is empty, or shorter than 4 lines,
collapse it instead of eating up screen real estate.

[1] made this possible.

[1]: #8028

front/src/styles/scss/applications/operationalStudies/_scenario.scss

@@ -116,7 +116,7 @@
       }
       .scenario-details-description {
         overflow: auto;
-        height: 4rem;
+        max-height: 4rem;
         font-size: 0.9rem;
         white-space: break-spaces;
       }