feat: add elasticsearch config and client

[rogercoll]

• Adds base code for embedding a Go configuration to create Elasticsearch clients. This initial PR contains some of the fields available in https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/exporter/elasticsearchexporter/config.go#L24
• The configelasticsearch package follows the same structure as upstream configuration packages: NewDefaultConfig + ToClient methods.

Usage (composed type so extra fields can be added):

type ElasticsearchClient struct {
	configelasticsearch.ClientConfig `mapstructure:",squash"`

	CacheDuration time.Duration `mapstructure:"cache_duration"`
}
esClient, err := cfg.Elasticsearch.ToClient(ctx, host, set.TelemetrySettings)

[carsonip]

code lgtm. Are you planning to make es exporter use this config and client?

[rogercoll]

code lgtm. Are you planning to make es exporter use this config and client?

The initial plan is to use it for a couple of extensions in Elastic's components repository, but yes, I will create an issue upstream to follow up on the exporter too.