[hotfix] Temporarily make it possible to build old documentation via GHA

We can't WebDav reliably to nightlies.apache.org, so we temporarily use the same mechanism that's used to build the docs to update the necessary fixes for release-1.13 until release-1.18

We need to add rsync to the docker image too to make this work

Author: MartijnVisser

.github/workflows/docs-legacy.yml

@@ -56,7 +56,7 @@ jobs:
             --volume "$PWD:/root/flink" \
             --volume "$HOME/.m2/repository:/root/.m2/repository" \
             chesnay/flink-ci:java_8_11_17_21_maven_386_jammy \
-            bash -c "cd /root/flink && ./.github/workflows/docs.sh"
+            bash -c "apt-get update && apt-get install -y rsync && cd /root/flink && ./.github/workflows/docs.sh"
 
       - name: Upload documentation
         uses: burnett01/rsync-deployments@0dc935cdecc5f5e571865e60d2a6cdc673704823 # 5.2