API server should have a dedicated user in Elasticsearch

[zaychenko-sergei]

Currently, API server connects to Elasticsearch via cluster admin credentials.

TODO in this ticket:

• Research Elasticsearch configuration / administration mechanisms regarding users and access permissions, in particular, in Elasticsearch Kubernetes operator
• Find an IaC-style solution to allow API server enough CRUD operations it needs over indices, aliases, ... but no administrative functions
• Extend configuration model, if needed (such as propagating user name) for plugging
• Deployment with adjustments