Enable Echidna auto-publishing.

.github/workflows/echidna.yml

@@ -0,0 +1,21 @@
+name: Publish to W3C
+on:
+  push:
+    branches: [main]
+jobs:
+  main:
+    name: Build, Validate, and Deploy
+    runs-on: ubuntu-20.04
+    steps:
+      - name: Checkout source code
+        uses: actions/checkout@v3
+      - name: Publish as W3C Technical Report Snapshot
+        uses: w3c/spec-prod@v2
+        if: ${{ github.ref_name == 'main' }}
+        with:
+          TOOLCHAIN: respec
+          W3C_ECHIDNA_TOKEN: ${{ secrets.W3C_TR_TOKEN }}
+          W3C_WG_DECISION_URL: https://www.w3.org/2017/vc/WG/Meetings/Minutes/2023-04-12-vcwg#resolution1
+          W3C_BUILD_OVERRIDE: |
+             shortName: controller-document
+             specStatus: WD