Add support for 'aws_credential_provider'

[annuh]

Fixes #1596

This adds support for the aws_credential_provider setting in Elastica, which was added in ruflin/Elastica#1667

Example usage:

// config/packages/fos_elastica.yaml
fos_elastica:
    clients:
        default:
            host: '%env(ELASTICSEARCH_HOST)%'
            port: '%env(ELASTICSEARCH_PORT)%'
            transport: "AwsAuthV4"
            aws_region: "eu-central-1"
            aws_credential_provider: 'aws.credentials_provider'

services:

    Aws\Credentials\CredentialProvider:
    aws.credentials_provider:
        class: 'Aws\Credentials\CredentialProvider'
        factory: [ '@Aws\Credentials\CredentialProvider', 'defaultProvider' ]

[XWB]

👍