Document SSH connector usage for docker-plugin in JCasC (fixes #2739)

demos/docker-plugin/README.md

@@ -0,0 +1,20 @@
+# Docker Plugin — SSH Connector JCasC Demo
+
+This demo provides a working Jenkins Configuration as Code (JCasC) example for configuring
+the Docker plugin with the SSH connector. The existing documentation does not show how to
+set up SSH-based agents using the docker-plugin, so this example is added to fill that gap.
+
+## SSH connector usage
+
+The docker-plugin exposes the `sshConnector` field for configuring SSH-based cloud agents.
+Using other keys such as `ssh:` does not match the expected structure and will cause a
+configuration error.
+
+A working configuration can be found in `docker-plugin-ssh.yaml`. The key part of the
+connector configuration is:
+
+```yaml
+connector:
+  sshConnector:
+    sshKeyCredentialsId: "my-ssh-key-id"
+    javaPath: "/opt/java/openjdk/bin/java"

demos/docker-plugin/docker-plugin.ssh.yaml

@@ -0,0 +1,20 @@
+# demos/docker-plugin/docker-plugin-ssh.yaml
+jenkins:
+  clouds:
+    - docker:
+        name: "my-docker-cloud"
+        dockerHost:
+          uri: "unix:///var/run/docker.sock"
+        templates:
+          - labelString: "worker1-agent"
+            dockerTemplateBase:
+              image: "jenkins/ssh-agent:latest-jdk17"
+              mounts:
+                - "type=tmpfs,destination=/run"
+                - "type=bind,source=/var/run/docker.sock,destination=/var/run/docker.sock"
+
+            remoteFs: "/home/jenkins/agent"
+            connector:
+              sshConnector:
+                sshKeyCredentialsId: "my-ssh-key-id"
+                javaPath: "/opt/java/openjdk/bin/java"

demos/jobs/multibranch-github.yaml

@@ -17,6 +17,8 @@ jobs:
           }
         }
         triggers {
-          periodic(5)
+        periodicFolderTrigger {
+        interval('5')
+          }
         }
-      }
+      }

demos/matrix-auth/README.md

@@ -1,5 +1,10 @@
 # matrix-auth-plugin
 
+> **Note:** Starting from **matrix-auth 3.2**, the older  
+> `grantedPermissions:` JCasC syntax is **deprecated**.  
+> The examples below already use the new **`entries:`** format, which should be used going forward.
+
+
 Configuration of the [Matrix Authorization Strategy plugin](https://plugins.jenkins.io/matrix-auth)
 
 There are a couple of built-in authorizations to consider.