Add elasticsearch Silta resources example

[misterjoonas]

Would be good to have some sane elasticsearch resources example. Something like this for production.

# Elasticsearch used for site search.
elasticsearch:
  # This value should be slightly less than 50% of the requested memory.
  esJavaOpts: -Xmx350m -Xms350m
  resources:
    requests:
      cpu: 250m
      memory: 750Mi
    limits:
      cpu: 500m
      memory: 1500Mi