DOCSP-27390 - Agg Expression Overview (#318)

* add new file

* JS MK feedback

Author: mongoKart

snooty.toml

@@ -17,6 +17,7 @@ sharedinclude_root = "https://raw.githubusercontent.com/10gen/docs-shared/main/"
 [constants]
 driver = "java"
 driver-long = "MongoDB Java Driver"
+driver-short = "Java Driver"
 version = "4.8"
 full-version = "{+version+}.2"
 mdb-server = "MongoDB server"

source/fundamentals/aggregation.txt

@@ -2,7 +2,9 @@
 Aggregation
 ===========
 
-.. default-domain:: mongodb
+.. toctree::
+
+   /fundamentals/aggregation/aggregation-expression-operations
 
 .. contents:: On this page
    :local:

source/fundamentals/aggregation/aggregation-expression-operations.txt

@@ -0,0 +1,32 @@
+=================================
+Aggregation Expression Operations
+=================================
+
+.. contents:: On this page
+   :local:
+   :backlinks: none
+   :depth: 2
+   :class: singlecol
+
+Overview
+--------
+
+In this guide, you can learn how to use the {+driver-long+} to construct expressions 
+for use in the aggregation pipeline. 
+With the {+driver-short+}, you can perform expression operations with
+discoverable, typesafe Java methods rather than BSON documents.
+Because these methods follow the fluent interface pattern, you can chain 
+aggregation operations together to create code that is both more compact and 
+more naturally readable.  
+
+.. tip:: 
+
+   For more information about aggregation expressions that use the Query API, see the 
+   :manual:`Aggregation Pipeline Operators </reference/operator/aggregation/>` 
+   page in the Server manual.
+
+Operations
+----------
+
+More Information
+----------------