Adding documentation for dangling index api (#1370)

* adding documentation for dangling index api

Signed-off-by: ariamarble <armarble@amazon.com>

* made editorial changes

Signed-off-by: ariamarble <armarble@amazon.com>

Signed-off-by: ariamarble <armarble@amazon.com>

_opensearch/rest-api/index-apis/dangling-index.md

@@ -0,0 +1,85 @@
+---
+layout: default
+title: Dangling indexes
+parent: index-apis
+grand_parent: REST API reference
+nav_order: 84
+---
+
+# Dangling indexes API
+
+After a node joins a cluster, dangling indexes occur if any shards exist in the node's local directory that do not already exist in the cluster. Dangling indexes can be listed, deleted, or imported.
+
+## Path and HTTP methods
+
+List dangling indexes:
+
+```
+GET /_dangling
+```
+
+Import a dangling index:
+
+```
+POST /_dangling/<index-uuid>
+```
+
+Delete a dangling index:
+
+```
+DELETE /_dangling/<index-uuid>
+```
+
+## Path parameters
+
+Path parameters are required.
+
+Path parameter | Description
+:--- | :---
+index-uuid | UUID of index.
+
+## Query parameters
+
+Query parameters are optional.
+
+Query parameter | Data Type | Description
+:--- | :--- | :---
+accept_data_loss | Boolean | Must be set to `true` for an `import` or `delete` because Opensearch is unaware of where the dangling index data came from.
+timeout | Time units | The amount of time to wait for a response. If no response is received in the defined time period, an error is returned. Default is `30` seconds.
+master_timeout | Time units | The amount of time to wait for the connection to the cluster manager. If no response is received in the defined time period, an error is returned. Default is `30` seconds.
+
+## Examples
+
+The following are sample requests and a sample response.
+
+#### Sample list
+
+````bash
+GET /_dangling
+````
+
+#### Sample import
+
+````bash
+POST /_dangling/msdjernajxAT23RT-BupMB?accept_data_loss=true
+````
+ 
+#### Sample delete
+
+````bash
+DELETE /_dangling/msdjernajxAT23RT-BupMB?accept_data_loss=true
+````
+
+#### Sample response body
+
+````json
+{
+    "_nodes": {
+        "total": 1,
+        "successful": 1,
+        "failed": 0
+    },
+    "cluster_name": "opensearch-cluster",
+    "dangling_indices": [msdjernajxAT23RT-BupMB]
+}
+````