disable autogeneration of secret each time the chart is deployed

[oklippel]

• [/] Chart version not bumped (the versions are all bumped and released at the same time)
• README.md updated with any new values or changes
• Updated template tests in ${CHART}/tests/*.py
• Updated integration tests in ${CHART}/examples/*/test/goss.yaml

Improved security password generation, see:
https://itnext.io/manage-auto-generated-secrets-in-your-helm-charts-5aee48ba6918
For detailed information, why this might be useful.

[elasticmachine]

Since this is a community submitted pull request, a Jenkins build has not been kicked off automatically. Can an Elastic organization member please verify the contents of this patch and then kick off a build manually?