allow using filter_path for /_cat/shards

README.md

@@ -81,6 +81,12 @@ Scraping `/stats` for `total.indexing` and `total.search` metrics only
 $ docker run --network=host -it vinted/elasticsearch_exporter --elasticsearch_url=http://IP:PORT --exporter_metrics_enabled="stats=true" --elasticsearch_query_filter_path="stats=indices.*.total.indexing,indices.*.total.search" 
 ```
 
+Scraping `/_cat/shards` for `search.fetch*` metrics only. In this case `elasticsearch_query_filter_path` must always include `index,shard`, and dotted format is not supported. Example: 
+
+```
+$ docker run --network=host -it vinted/elasticsearch_exporter --elasticsearch_url=http://IP:PORT --exporter_metrics_enabled="cat_shards=true" --elasticsearch_query_filter_path="cat_shards=index,shard,search*fetch*" 
+```
+
 ```shell
 $ curl -s http://127.0.0.1:9222
 Vinted Elasticsearch exporter

src/metrics/_cat/shards.rs

@@ -6,17 +6,23 @@ use super::responses::CatResponse;
 pub(crate) const SUBSYSTEM: &str = "cat_shards";
 
 async fn metrics(exporter: &Exporter) -> Result<Vec<Metrics>, elasticsearch::Error> {
-    let response = exporter
-        .client()
-        .cat()
+    let filter_path = exporter.options().query_filter_path_for_subsystem(SUBSYSTEM);
+
+    let cat = exporter.client().cat();
+
+    let mut shards_stats = cat
         .shards(CatShardsParts::Index(&["*"]))
         .format("json")
         .h(&["*"])
         .bytes(Bytes::B)
         .request_timeout(exporter.options().timeout_for_subsystem(SUBSYSTEM))
-        .time(Time::Ms)
-        .send()
-        .await?;
+        .time(Time::Ms);
+
+    if !filter_path.is_empty() {
+        shards_stats = shards_stats.filter_path(&filter_path)
+    }
+
+    let response = shards_stats.send().await?;
 
     let values = response.json::<CatResponse>().await?.into_values(|map| {
         if map