Add Documentation for sample UKI Generation

docs/generate_sample_uki.md

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+### How to Generate a UKI Image for HTTPBoot with Gardenlinux
+
+#### Step 1: Prerequisites
+- Ensure you have the `ukify` tool installed on your system. This tool is essential for creating the UKI image.
+- You will need administrative or root privileges to execute most of the commands described.
+
+#### Step 2: Download and Prepare Gardenlinux Release
+1. Download the appropriate Gardenlinux release for your architecture. For example, a metal-based system with an AMD64 architecture, use the following command:
+   ```bash
+   wget https://github.com/gardenlinux/gardenlinux/releases/download/1443.10/metal-gardener_prod_pxe-amd64-1443.10-8d098305.tar.xz
+   ```
+2. Extract the downloaded `.tar.xz` file:
+   ```bash
+   tar -xvf metal-gardener_prod_pxe-amd64-1443.10-8d098305.tar.xz
+   ```
+3. Further extract the nested `*.pxe.tar.gz` which contains the kernel and initial RAM disk:
+   ```bash
+   tar -xzf <nested_tar_name>.pxe.tar.gz
+   ```
+   You should see files like `vmlinuz`, `initrd`, and `root.squashfs`.
+
+#### Step 3: Obtain the Bootloader Stub
+Download the EFI stub required for the UKI creation:
+```bash
+tbd
+```
+
+#### Step 4: Create the UKI Image
+Construct the UKI image using the `ukify` command. Ensure to replace placeholders with actual paths and URLs:
+```bash
+ukify build --stub "/path/to/stub" --linux "/path/to/vmlinuz" --initrd "/path/to/initrd" --cmdline "@cmdline" --output "/path/to/output/test.uki"
+
+# Create file with the name cmdline, with following content
+# Use this as the sample command line, replace URLs and paths as necessary
+initrd=/path/to/initrd gl.ovl=/:tmpfs gl.live=1 ip=dhcp console=ttyS0,115200 console=tty0 earlyprintk=ttyS0,115200 consoleblank=0 ignition.firstboot=1 ignition.config.url=IGNITION_URL ignition.platform.id=metal gl.url=SQUASHFS_URL
+```
+
+#### Step 5: Deploy the Image to a Server
+Copy the created `test.uki` to an Nginx server configured to serve the files:
+```bash
+cp /path/to/output/test.uki /path/to/nginx/server/httpboot/test-uki.efi
+# Also, ensure the squashfs file is accessible via HTTP
+cp /path/to/root.squashfs /path/to/nginx/server/httpboot/squashfs
+```
+Ensure EFI files are served by NGINX with the correct content-type.
+```bash
+ application/efi efi;
+```
+
+#### Step 6: Configure HTTPBoot
+Create a YAML configuration for the HTTPBoot client. Replace placeholders as required:
+```yaml
+apiVersion: boot.ironcore.dev/v1alpha1
+kind: HTTPBootConfig
+metadata:
+  name: httpbootconfig-sample
+  namespace: boot-operator-system
+spec:
+  ignitionSecretRef:
+    name: ignition-http-sample
+    namespace: boot-operator-system
+  systemUUID: "generate-this-uuid"
+  systemIPs:
+    - "1.1.1.1"
+    - "ip/mac-address-of-interfaces"
+  ukiURL: "http://[your-server-ip-or-domain]/httpboot/test-uki.efi"
+```
+
+Apply this configuration to your cluster and ensure the metal machine is set to boot via HTTPBoot.