Update ElasticSearch to 6.8.23 in the Dockerfile and update Elastica to
6.x in composer.

- 'inline' scripts are deprecated, changed to 'source'

Update arElasticSearchPlugin to use multiple indices instead of multiple
types since ES 6.x removed being able to add multiple types. Also update
mapping to remove include_in_all and add that to the _all field using
copy_to instead since include_in_all was also removed in ES 6.x

Update autocompleteAction to use multiple indices

Add the appropriate index types for ES requests that did not need to
specify explicit types in ES 5.x

Add missing document type to partialUpdate in arElasticSearchPlugin

Update condition in arElasticSearchPluginUtil to only get string
fields included in _all if copy_to is explicitly set to _all in the
mappping.

Renamed arElasticSearchIndexDecorator as
arElasticSearchMultiIndexWrapper for clarity and added a few comments
about changes needed for ElasticSearch/Elastica 7.x.

Rename getType from arElasticSearchMultiIndexWrapper to getIndex for
clarity.

Add a dummy ElasticSearch index type since one is still required for
ES 6.x, instead of having a seperate type name for each of the
multiple indices.