Doc enhancement for eventstats and bin command (opensearch-project#4117)

* distinct_count doc for eventstats

Signed-off-by: Kai Huang <ahkcs@amazon.com>

* doc enhancement

Signed-off-by: Kai Huang <ahkcs@amazon.com>

* add fields for consistency between different Java versions

Signed-off-by: Kai Huang <ahkcs@amazon.com>

* remove changes

Signed-off-by: Kai Huang <ahkcs@amazon.com>

* add bin to index.rst

Signed-off-by: Kai Huang <ahkcs@amazon.com>

* add link

Signed-off-by: Kai Huang <ahkcs@amazon.com>

* fix

Signed-off-by: Kai Huang <ahkcs@amazon.com>

---------

Signed-off-by: Kai Huang <ahkcs@amazon.com>

Author: ahkcs

docs/user/ppl/cmd/bin.rst

@@ -9,6 +9,11 @@ bin
    :depth: 2
 
 
+.. note::
+   
+   Available since version 3.3
+
+
 Description
 ============
 | The ``bin`` command groups numeric values into buckets of equal intervals, making it useful for creating histograms and analyzing data distribution. It takes a numeric field and generates a new field with values that represent the lower bound of each bucket.

docs/user/ppl/cmd/eventstats.rst

@@ -283,7 +283,10 @@ DISTINCT_COUNT, DC(Since 3.3)
 Description
 >>>>>>>>>>>
 
-Usage: DISTINCT_COUNT(expr), DC(expr). Returns the approximate number of distinct values of expr using HyperLogLog++ algorithm. Both ``DISTINCT_COUNT`` and ``DC`` are equivalent and provide the same functionality.
+Usage: DISTINCT_COUNT(expr), DC(expr). Returns the approximate number of distinct values using the HyperLogLog++ algorithm. Both functions are equivalent.
+
+For details on algorithm accuracy and precision control, see the `OpenSearch Cardinality Aggregation documentation <https://docs.opensearch.org/latest/aggregations/metric/cardinality/#controlling-precision>`_.
+
 
 Example::
 

docs/user/ppl/index.rst

@@ -54,6 +54,8 @@ The query start with search command and then flowing a set of command delimited
 
   - `appendcol command <cmd/appendcol.rst>`_
 
+  - `bin command <cmd/bin.rst>`_
+
   - `dedup command <cmd/dedup.rst>`_
 
   - `describe command <cmd/describe.rst>`_