ci: allow custom kernel and target jobs based on labels

Current job triggers based on matching of changed paths is quite
limited, so lets make it possible to additionally trigger manual CI jobs
by adding CI specific pull request build labels:

 * `ci:target:x86:64` label is going to trigger CI target check jobs for
    x86/64 (sub)target.

 * `ci:kernel:x86:64` label is going to trigger CI kernel check jobs for
    x86/64 (sub)target.

Signed-off-by: Petr Štetiar <ynezz@true.cz>

.github/workflows/label-kernel.yml

@@ -0,0 +1,45 @@
+# ci:kernel:x86:64 is going to trigger CI kernel check jobs for x86/64 target
+
+name: Build kernel and check patches for target specified in labels
+on:
+  pull_request:
+    types:
+      - labeled
+
+jobs:
+  set_target:
+    if: startsWith(github.event.label.name, 'ci:kernel:')
+    name: Set target
+    runs-on: ubuntu-latest
+    outputs:
+      target: ${{ steps.set_target.outputs.target }}
+
+    steps:
+      - name: Set target
+        id: set_target
+        env:
+          CI_EVENT_LABEL_NAME: ${{ github.event.label.name }}
+        run: |
+          echo "$CI_EVENT_LABEL_NAME" | sed -n 's/.*:\(.*\):\(.*\)$/target="\1\/\2"/p' | tee --append $GITHUB_OUTPUT
+
+  build_kernel:
+    name: Build Kernel with external toolchain
+    needs: set_target
+    permissions:
+      contents: read
+      packages: read
+    uses: ./.github/workflows/build.yml
+    with:
+      target: ${{ needs.set_target.outputs.target }}
+      build_kernel: true
+      build_all_kmods: true
+
+  check-kernel-patches:
+    name: Check Kernel patches
+    needs: set_target
+    permissions:
+      contents: read
+      packages: read
+    uses: ./.github/workflows/check-kernel-patches.yml
+    with:
+      target: ${{ needs.set_target.outputs.target }}

.github/workflows/label-target.yml

@@ -0,0 +1,37 @@
+# ci:target:x86:64 is going to trigger CI target check jobs for x86/64 target
+
+name: Build check target specified in labels
+on:
+  pull_request:
+    types:
+      - labeled
+
+jobs:
+  set_target:
+    if: startsWith(github.event.label.name, 'ci:target:')
+    name: Set target
+    runs-on: ubuntu-latest
+    outputs:
+      target: ${{ steps.set_target.outputs.target }}
+
+    steps:
+      - name: Set target
+        id: set_target
+        env:
+          CI_EVENT_LABEL_NAME: ${{ github.event.label.name }}
+        run: |
+          echo "$CI_EVENT_LABEL_NAME" | sed -n 's/.*:\(.*\):\(.*\)$/target="\1\/\2"/p' | tee --append $GITHUB_OUTPUT
+
+  build_target:
+    name: Build target
+    needs: set_target
+    permissions:
+      contents: read
+      packages: read
+    uses: ./.github/workflows/build.yml
+    with:
+      target: ${{ needs.set_target.outputs.target }}
+      build_full: true
+      build_all_kmods: true
+      build_all_boards: true
+      build_all_modules: true