Auto-generate release notes (#526)

This uses the same mechanism as Boulder does.

Author: aarongable

.github/workflows/release.yml

@@ -138,12 +138,7 @@ jobs:
         # https://cli.github.com/manual/gh_release_create
         env:
           GITHUB_TOKEN: ${{ github.token }}
-        run: |
-          gh release create ${{ github.ref_name }} \
-            --repo ${{ github.repository }} \
-            --title "${{ github.ref_name }}" \
-            --verify-tag
-        continue-on-error: true
+        run: gh release create --generate-notes --verify-tag ${GITHUB_REF_NAME}
       - name: Upload release files
         # https://cli.github.com/manual/gh_release_upload
         env: