Add article on tekton pipelines with git clone example (#277)

Co-authored-by: Richard Hagen <[email protected]>

public-site/docs/src/guides/sub-pipeline/example-pipeline-with-deploy-keys.md

@@ -0,0 +1,90 @@
+---
+title: "Sub-pipeline example: Pipeline with GitHub deploy keys"
+---
+
+# Sub-pipeline example: Pipeline with GitHub deploy keys
+
+* In the Radix application repository create a folder `tekton`. This folder need to be in the configuration branch and in the same folder, where `radixconfig.yaml` file is located (by default it is a root of the repository).
+* The sub-pipeline in this example runs one task with two steps.
+* Create a file `test-github.yaml` for the task `test-github`. This task has two steps "git-clone" and a step "list-contents".
+
+:::tip
+Mount a volume named `$(radix.git-deploy-key)` where you need you ssh credentials.
+:::
+
+File `test-github.yaml`
+
+```yaml
+apiVersion: tekton.dev/v1
+kind: Task
+metadata:
+  name: test-github
+spec:
+  stepTemplate:
+    image: alpine/git
+    volumeMounts:
+      - name: source-volume
+        mountPath: /var/source
+    securityContext:
+      runAsUser: 65534 # nobody
+
+  steps:
+    - name: git-clone
+      volumeMounts:
+        - name: $(radix.git-deploy-key) # <-- This volume is created by Radix and available where you mount it.
+          mountPath: /.ssh
+      command:
+        - git
+        - clone
+        - [email protected]:Equinor-Playground/rihag-edc23-radix-1.git
+        - /var/source/branch
+
+    - name: list-contents
+      script: |
+        #!/usr/bin/env sh
+        ls -la /var/source/branch
+
+  volumes:
+    - name: source-volume
+      emptyDir: { }
+
+```
+
+* Create a file `pipeline.yaml`. Add a task in the `tasks` list: give it a name (it can be any name, unique within this sub-pipeline), in the property `taskRef` ("reference to a task") put the value from the property `metadata.name` of the task, created above:
+
+```yaml
+apiVersion: tekton.dev/v1
+kind: Pipeline
+metadata:
+  name: test-pipeline
+spec:
+  tasks:
+    - name: test-github
+      taskRef:
+        name: test-github
+
+```
+
+* File structure can be like this:
+
+```sh
+/
+├── tekton/
+│   ├── pipeline.yaml
+│   └── test-github.yaml
+└── radixconfig.yaml
+```
+
+## Details:
+  * The userid `65534` is mapped to the user `nobody` in the image `alpine/git`, with the home folder set to `/`
+  * The volume referenced by `$(radix.git-deploy-key)` is mounted read-only and both files, `id_rsa` and `known_hosts` have permission level `444`, owned by `root:root`. 
+    ```shell
+    total 4
+    drwxrwxrwt    3 root     root           120 Nov 16 09:06 .
+    drwxr-sr-x    1 git      git           4096 Nov 16 09:06 ..
+    drwxr-xr-x    2 root     root            80 Nov 16 09:06 ..2023_11_16_09_06_55.2062090024
+    lrwxrwxrwx    1 root     root            32 Nov 16 09:06 ..data -> ..2023_11_16_09_06_55.2062090024
+    lrwxrwxrwx    1 root     root            13 Nov 16 09:06 id_rsa -> ..data/id_rsa
+    lrwxrwxrwx    1 root     root            18 Nov 16 09:06 known_hosts -> ..data/known_hosts
+    ```
+    Note that the permissions listed are wrong, and the underlaying data have limited permissions.

public-site/docs/src/guides/sub-pipeline/index.md

@@ -137,3 +137,4 @@ In Radix platform, the following limitations are applied to sub-pipelines:
 * [Sub-pipeline with build environment variables](./example-pipeline-with-env-vars.md)
 * [Sub-pipeline with build environment variables for environments](./example-pipeline-with-env-vars-for-envs.md)
 * [Sub-pipeline with build secrets](./example-pipeline-with-build-secrets.md)
+* [Sub-pipeline with GitHub deploy keys](./example-pipeline-with-deploy-keys.md)