Add: [JenkinsFile] show CI status per entry on GitHub

This makes it easier (and faster) to spot what went wrong

Jenkinsfile

@@ -16,6 +16,9 @@ def ci_builds_stages = ci_builds_targets.collectEntries {
 
 def generateCI(display_name, image_name) {
     return {
+        githubNotify context: 'openttd/' + display_name, description: 'This commit is being built', status: 'PENDING'
+
+        try {
             dir("${display_name}") {
                 unstash "source"
 
@@ -24,6 +27,13 @@ def generateCI(display_name, image_name) {
                     sh "exit `docker wait ${c.id}`"
                 }
             }
+
+            githubNotify context: 'openttd/' + display_name, description: 'The commit looks good', status: 'SUCCESS'
+        }
+        catch (error) {
+            githubNotify context: 'openttd/' + display_name, description: 'The commit cannot be built', status: 'FAILURE'
+            throw error
+        }
     }
 }