[dependency] pin python-elasticsearch and python-elasticsearch-dsl versions as elasticsearch 7 has been released

previously bool value was 0 or 1 it seems that elasticsearch 6 will not cast
this value anymore

this magic field does not exist anymore with elasticsearch 6 use computed field which it is named alltext by convention

this magic field does not exist anymore with elasticsearch 6
use computed field which it is named `alltext` by convention

[elasticserach] elasticsearch.client.Elasticsearch.index expect a string as value of `refresh` param

Starting from ES6, `_type` metadata is deprecated,
cf. https://www.elastic.co/guide/en/elasticsearch/reference/current/removal-of-types.html

If this is not done, elasticsearch.scan method retrieves the old index values
so wrong values will be copied while synchronizing different indexes.

We probably should do it by default in `indexer.es_index` method.
We probably should do it in `indexer.es_delete` method.

see also https://www.elastic.co/guide/en/elasticsearch/reference/current/docs-refresh.html

related to #17090555

When indexing an entity type, don't generate a single
and possibly huge rset with all entities of that type.
Instead, fetch entities chunk by chunk and free caches
between each round.

closes #17090555

ESTransactionQueue batches all ES operations on postcommit.

Client cubes could override the default logic to add, log,
ditch… any other operation.

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

For optimization sake, just make sure the original rset
fetches everyting or use complete=True but relying on
cw_attr_cache will cause very obscure bugs

closes #17079907

* 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

otherwise the import just hand forever.