[kots] load custom docker config correctly

This PR fixes the issue when a custom docker config json file is uploaded by the user. Signed-off-by: Tarun Pothulapati <tarun@gitpod.io>

Author: Pothulapati

install/installer/scripts/kots-install.sh

@@ -162,6 +162,7 @@ EOF
  | base64 -d \
  > /tmp/currentconfig.json
 
+ echo "${REGISTRY_DOCKER_CONFIG_JSON}" > /tmp/userconfig.json
  echo "Gitpod: update the in-cluster registry secret"
  REGISTRY_SECRET="$(jq -s '.[0] * .[1]' /tmp/userconfig.json /tmp/currentconfig.json | base64 -w 0)"
  export REGISTRY_SECRET