feat: scrape number_of_replicas and number_of_shards

[scor2k]

Scrape number_of_replicas and number_of_shards metrics when --es.indices_settings provided

# HELP elasticsearch_indices_settings_number_of_shards number of index shards
# TYPE elasticsearch_indices_settings_number_of_shards gauge
elasticsearch_indices_settings_number_of_shards{index=".kibana_1"} 1
elasticsearch_indices_settings_number_of_shards{index=".kibana_task_manager"} 1
elasticsearch_indices_settings_number_of_shards{index="logs-common-"} 5
elasticsearch_indices_settings_number_of_shards{index="logs-common-2021.11.01"} 5
elasticsearch_indices_settings_number_of_shards{index="logs-common-2021.11.03"} 5
elasticsearch_indices_settings_number_of_shards{index="logs-common-2021.11.04"} 5

# HELP elasticsearch_indices_settings_number_of_replicas index number of replicas
# TYPE elasticsearch_indices_settings_number_of_replicas gauge
elasticsearch_indices_settings_number_of_replicas{index=".kibana_1"} 0
elasticsearch_indices_settings_number_of_replicas{index=".kibana_task_manager"} 0
elasticsearch_indices_settings_number_of_replicas{index="logs-common-"} 1
elasticsearch_indices_settings_number_of_replicas{index="logs-common-2021.11.01"} 1
elasticsearch_indices_settings_number_of_replicas{index="logs-common-2021.11.03"} 1
elasticsearch_indices_settings_number_of_replicas{index="logs-common-2021.11.04"} 1

Closes https://github.com/prometheus-community/elasticsearch_exporter/issues/482