bug 1094767; crashstorage type for new ES module

This PR introduces a crashstorage type for the new ES module.  It also modifies the `ConnectionContext` class to bring it in line with the patterns established in the other `external` modules.  The changes to the context required some other modifications to be made to the index creation class (and associated tests).

`r?` @AdrianGaudebert @twobraids 
This was not addressed. The config options in this class are not shared by all Elasticsearch-based resources, they belong only to the processor, and thus should not be put in ``resource.elasticsearch``. You can simply remove this line here and line 35 below to fix it.