Okay I tried, it works with :

apiserver:
  extraEnvs:
    - name: CLEARML_ELASTIC_SERVICE_USERNAME
      value: "elastic"
    - name: CLEARML_ELASTIC_SERVICE_PASSWORD
      value: "toto"

But we don't need to add the option into elasticsearchConnectionString :

externalServices:
    elasticsearchConnectionString: "[...,"secure":true,...]"

As we get this error :

ValueError: Can't specify the options 'secure' via a dictionary in 'hosts', only 'host', 'path_prefix', 'port', 'scheme', 'url_prefix', 'use_ssl' options are allowed

It works fine, thank you very much 😉