.github: Build PXE image as additional VM image format

The PXE image and its helper script is a very handy way to test an image
because it does not preserve state. One can boot the same file over and
over again without having to reset the image. One can also easily pass
in additional kernel cmdline options without having to set up grub.cfg.

.github/workflows/ci.yaml

@@ -7,7 +7,7 @@ on:
         description: |
           Space-separated vendor formats to build.
         required: true
-        default: qemu_uefi
+        default: qemu_uefi pxe
       custom_sdk_version:
         type: string
         required: false
@@ -21,7 +21,7 @@ on:
         description: |
           Space-separated vendor formats to build.
         required: true
-        default: qemu_uefi
+        default: qemu_uefi pxe
       custom_sdk_version:
         type: string
         required: false
@@ -96,7 +96,7 @@ jobs:
           arch="${{ matrix.arch }}"
           echo "arch=${arch}" >> $GITHUB_ENV
 
-          IMAGE_FORMATS="qemu_uefi"
+          IMAGE_FORMATS="qemu_uefi pxe"
           [ -z "${{ inputs.image_formats }}" ] || IMAGE_FORMATS="${{ inputs.image_formats }}"
           echo "IMAGE_FORMATS=${IMAGE_FORMATS}" >> $GITHUB_ENV
 

.github/workflows/pr-comment-build-dispatcher.yaml

@@ -77,4 +77,4 @@ jobs:
     uses: ./.github/workflows/ci.yaml
     with:
       custom_sdk_version: ${{ needs.update_sdk.outputs.sdk_version }}
-      image_formats: qemu_uefi
+      image_formats: qemu_uefi pxe

.github/workflows/pr-workflows.yaml

@@ -46,4 +46,4 @@ jobs:
     uses: ./.github/workflows/ci.yaml
     with:
       custom_sdk_version: ${{ needs.update_sdk.outputs.sdk_version }}
-      image_formats: qemu_uefi
+      image_formats: qemu_uefi pxe