[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

Author: MartijnVisser

.github/workflows/docs-legacy.yml

@@ -0,0 +1,70 @@
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You under the Apache License, Version 2.0
+# (the "License"); you may not use this file except in compliance with
+# the License.  You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+name: "Build legacy documentation"
+on:
+  workflow_dispatch:
+    inputs:
+      branch:
+        description: 'Branch to build documentation for'
+        required: true
+        type: choice
+        options:
+          - release-1.18
+          - release-1.17
+          - release-1.16
+          - release-1.15
+          - release-1.14
+          - release-1.13
+
+jobs:
+  build-documentation:
+    if: github.repository == 'apache/flink'
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          ref: ${{ inputs.branch }}
+
+      - name: Set branch environment variable
+        run: |
+          echo "flink_branch=${{ inputs.branch }}" >> ${GITHUB_ENV}
+
+      - name: Cache Maven dependencies
+        uses: actions/cache@v4
+        with:
+          path: ~/.m2/repository
+          key: ${{ runner.os }}-maven-docs-${{ hashFiles('**/pom.xml') }}
+          restore-keys: |
+            ${{ runner.os }}-maven-docs-
+
+      - name: Build documentation
+        run: |
+          docker run --rm \
+            --volume "$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"
+
+      - name: Upload documentation
+        uses: burnett01/rsync-deployments@0dc935cdecc5f5e571865e60d2a6cdc673704823 # 5.2
+        with:
+          switches: --archive --compress --delete
+          path: docs/target/
+          remote_path: ${{ secrets.NIGHTLIES_RSYNC_PATH }}/flink/flink-docs-${{ env.flink_branch }}/
+          remote_host: ${{ secrets.NIGHTLIES_RSYNC_HOST }}
+          remote_port: ${{ secrets.NIGHTLIES_RSYNC_PORT }}
+          remote_user: ${{ secrets.NIGHTLIES_RSYNC_USER }}
+          remote_key: ${{ secrets.NIGHTLIES_RSYNC_KEY }}