[ci] Add a job to automatically create releases

Add a job that will automatically create a (draft) release for any
suitable tag, using the build artifacts and release notes already
constructed by earlier jobs.  Minimise the logic within the release
job itself, since by definition it cannot be tested on every commit.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

.github/workflows/build.yml

@@ -522,7 +522,8 @@ jobs:
       - name: Build
         working-directory: src
         run: |
-          make ${{ env.bindir }}/version.txt \
+          make REPOURL=${{ github.server_url }}/${{ github.repository }} \
+               ${{ env.bindir }}/version.txt \
                ${{ env.bindir }}/relname.txt \
                ${{ env.bindir }}/reltitle.txt \
                ${{ env.bindir }}/relnotes.md
@@ -579,3 +580,43 @@ jobs:
         run: |
           gh workflow run build.yml -f run_id=${{ github.run_id }}
           echo "Results at ${{ env.workflow_url }}"
+
+  release:
+    name: Release
+    runs-on: ubuntu-latest
+    needs:
+      - bios
+      - sbi
+      - uefi
+      - sbsign
+      - linux
+      - shim
+      - combine
+      - netboot
+      - version
+    if: >-
+      startsWith ( github.ref, 'refs/tags/v' )
+    steps:
+
+      - name: Download
+        uses: actions/download-artifact@v7
+        with:
+          pattern: "{bin-combi,netboot,version}"
+
+      - name: Tag check
+        run: |
+          RELNAME=$(cat version/relname.txt)
+          if [ "${{ github.ref_name }}" != "${RELNAME}" ] ; then
+              echo "ERROR: Tag does not match release name ${RELNAME}" >&2
+              exit 1
+          fi
+
+      - name: Release
+        env:
+          GH_REPO: ${{ github.repository }}
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          gh release create "${{ github.ref_name }}" --verify-tag --draft \
+              --title "$(cat version/relname.txt)" \
+              --notes-file version/relnotes.md \
+              bin-combi/ipxe.iso bin-combi/ipxe.usb netboot/ipxeboot.tar.gz