ci: Introduce lychee to check links

Use `lychee` to check availability of links in cloud-hypervisor.

The urls explictly excluded in config file are manually checked.

Signed-off-by: Ruoqing He <heruoqing@iscas.ac.cn>

.github/workflows/lychee.yaml

@@ -0,0 +1,16 @@
+name: Link Check (lychee)
+on:
+  pull_request
+
+jobs:
+  link_check:
+    name: Link Check
+    runs-on: ubuntu-latest
+    steps:
+      - name: Code checkout
+        uses: actions/checkout@v4
+
+      - name: Link Availability Check
+        uses: lycheeverse/lychee-action@master
+        with:
+          args: --verbose --config .lychee.toml .