CI: added line length validation

Author: glpatcern

.github/workflows/line-length.yml

@@ -0,0 +1,13 @@
+name: Validate I-D line length
+on: [push]
+
+jobs:
+  validate_line_length:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Validate I-D line length
+        run: grep -nE '.{73,}' IETF-RFC.md | grep ' ' || exit -1
+