Indexer instances are the ones who know how to connect
to elasticsearch and which index should the query should
be executed on

As for ES "id" parameters, "doc_type" should be customizable,
there is no reason why es document type should match cw_etype

Default is to use 'eid' but one may want to use something
else (stable id, ark, etc.)

closes #17079908

* get rid of CUSTOM_ATTRIBUTES. Replace it with IFullTextIndexSerializable adapter `custom_indexable_attributes`
  attribute;
* FullTextIndexSerializable.serialize method : default complete value is now True*


closes #17079905

we should not crash if we try to delete an inexisting document

(closes #17071989)

let serializer decide if cw_etype and doc_type is different

precommit_event is too early to access in_state relation of workflowable entity

closes #17052625

In order to be sure that child / parent relation is set

Also : ccplugin - generator serves all actions, not split up by type
       es.py - add CUSTOM_ATTRIBUTES mechanism