GHA: convert download page update to a reusable shell script

.github/scripts/update-distro-download-page.sh

@@ -0,0 +1,19 @@
+dist_path=$1
+eclipse_version=$2
+build_type=$3
+
+s3_url=s3://dist.springsource.com/${dist_path}
+downloads_html="sts4-nightly-${eclipse_version}.html"
+files=`aws s3 cp ${s3_url} . --recursive --exclude "*" --include "spring-tool-suite-4*.zip" --include "spring-tool-suite-4*.dmg" --include "spring-tool-suite-4*.self-extracting.jar" --include "spring-tool-suite-4*.tar.gz" --exclude "*/*" --dryrun`
+echo '<ul>' >> $downloads_html
+for file in $files
+do
+  if [[ "$file" =~ ^"s3://dist." ]]; then
+    download_url=https://download${file:9}
+    filename=${file:${#s3_url}+1}
+    echo '  <li><a href="'${download_url}'">'${filename}'</li>' >> $downloads_html
+  fi
+done
+echo '</ul>' >> $downloads_html
+cat ./$downloads_html
+aws s3 mv ./$downloads_html s3://dist.springsource.com/${build_type}/STS4/ --acl public-read --no-progress