Removal of Elasticsearch environment variables means secrets have to be stored in code

Since v4.4 the individual environment variables for configuring Elasticsearch are obsolete. e.g. `ES_HOST`, `ES_PORT`, `ES_PASSWORD` etc.

This is a regression for us since we rely on passing secrets to individual environment variables from AWS secrets manager/parameter store using the "value_from" directive. See https://docs.aws.amazon.com/AmazonECS/latest/developerguide/secrets-envvar-ssm-paramstore.html#secrets-envvar-ssm-paramstore-update-container-definition

Since we now have to pass all Geonetwork settings in the one variable `GN_CONFIG_PROPERTIES` it makes it necessary to store the secret for `ES_PASSWORD` in plain-text in code, unless we store all the values for `GN_CONFIG_PROPERTIES` as a secret too. However this becomes annoying as we ideally want to be able to look at the code to see what a particular environment is using.

Is there a good reason why these variables were deprecated?

Start by reviewing the v4.4 Docker configuration and how ES_HOST, ES_PORT, ES_PASSWORD, and GN_CONFIG_PROPERTIES are processed. Compare that behavior with AWS ECS value_from secret injection. Done requires an agreed configuration approach that avoids putting ES_PASSWORD in source, or documentation explaining why the individual variables were removed.

Written by the indexing model from the issue text.