Added configurable options for basic http authentication for Elastic Api

[Nielex]

I added to possibility to use basic HTTP authentication. If you host your Elasticsearch instance on AWS or Elastic Cloud you want to use this.

I tested this for my instance on AWS and this works fine. This is related to this issue:
#211 (comment)

[afoucret]

Hi @Nielex, we will have a look at this when we will have the time.
It's seems the build is broken because of our coding standards convention are not fully respected :

Here is an extract of the build output :

FILE: ...asticsuite/src/module-elasticsuite-core/Client/ClientFactory.php
----------------------------------------------------------------------
FOUND 1 ERROR AFFECTING 1 LINE
----------------------------------------------------------------------
 94 | ERROR | [x] The closing brace for the class must go on the next
    |       |     line after the body
----------------------------------------------------------------------
PHPCBF CAN FIX THE 1 MARKED SNIFF VIOLATIONS AUTOMATICALLY
----------------------------------------------------------------------

[Nielex]

@afoucret

I fixed the error form the build output. I'll hope this will pass your tests.