Update get-helm-3 to get version through get.helm.sh

Updates the script to use the new method of getting
the latest version that avoids the github API and
the associated rate limits. See the matching PR
at #12396 for
the server side change.

Signed-off-by: Ian Zink <zforce@gmail.com>
(cherry picked from commit f94e5db)

scripts/get-helm-3

@@ -108,14 +108,14 @@ verifySupported() {
 checkDesiredVersion() {
   if [ "x$DESIRED_VERSION" == "x" ]; then
     # Get tag from release URL
-    local latest_release_url="https://api.github.com/repos/helm/helm/releases/latest"
+    local latest_release_url="https://get.helm.sh/helm-latest-version"
     local latest_release_response=""
     if [ "${HAS_CURL}" == "true" ]; then
       latest_release_response=$( curl -L --silent --show-error --fail "$latest_release_url" 2>&1 || true )
     elif [ "${HAS_WGET}" == "true" ]; then
       latest_release_response=$( wget "$latest_release_url" -O - 2>&1 || true )
     fi
-    TAG=$( echo "$latest_release_response" | grep '"tag_name"' | sed -E 's/.*"(v[0-9\.]+)".*/\1/g' )
+    TAG=$( echo "$latest_release_response" | grep '^v[0-9]' )
     if [ "x$TAG" == "x" ]; then
       printf "Could not retrieve the latest release tag information from %s: %s\n" "${latest_release_url}" "${latest_release_response}"
       exit 1