Feature: Pluggable client

[mgalang]

Problem/Motivation

Elasticsearch helper client currently has a somewhat hard dependency with the Elasticsearch PHP client. This works ok for most cases, but there has been cases where Elasticsearch is behind a proxy API, and the API has a different request format.

There has also been proposal for expanding the capabilities of the module to allow the use other search backend engines in the future. This would be a first step towards that direction also.

Proposed solution

• Refactor the client as a service
• Deprecate the old client builder
• Create a default client, which uses the Elasticsearch PHP client
• Add a client interface which would enforces the methods and attributes of existing and future clients
• Updated Index base class to use the new client and interface

I have added an example index that uses a custom client as an example of how to use this.

Possible issues

• This would create breaking changes for projects and modules that calls the client directly, or have implemented custom index methods