Add /build-info page displaying

Add page displaying information about the deployment for diagnostic
purposes.

.forgejo/workflows/build.yaml

@@ -22,8 +22,16 @@ jobs:
           echo "https://runner:${{ secrets.GITHUB_TOKEN }}@$(echo "${{ github.server_url }}" | cut -b 9-)" > ~/.git-credentials
           git clone --branch ${{ github.ref_name }} ${{ github.server_url }}/${{ github.repository }} ${{ github.workspace }}
       -
-        name: Build and push
+        name: Write build info
         shell: bash
+        run: |
+          cat > ${{ github.workspace }}/shared/utils/build-info.ts <<EOF
+          export const BUILDER = "forgejo-runner";
+          export const GIT_REF = "${{ github.ref_name }}";
+          export const GIT_SHA = "${{ github.sha }}";
+          EOF
+      -
+        name: Build and push
         run: |
           podman build --tag ${{ env.REGISTRY_IMAGE }} ${{ github.workspace }}
           podman push ${{ env.REGISTRY_IMAGE }}