DOCSP-44237 flags Option deprecation on v2.21 (#201)

* DOCSP-44237 flags Option deprecation on v2.21

* add what's new note

* Rea review comments

Author: lindseymoore

source/reference/method/MongoDBDatabase-createCollection.txt

@@ -152,6 +152,12 @@ Parameters
          :manual:`db.createCollection()
          </reference/method/db.createCollection>` for more information.
 
+         *Deprecated*: This option is deprecated and will be removed in 
+         the v2.0 {+library-short+} release. To learn more about upgrading 
+         from the MMAPv1 storage engine to Wired Tiger, see the 
+         :manual:`Change a Self-Managed Standalone to WiredTiger </tutorial/change-standalone-wiredtiger/>` 
+         guide in the Server manual.
+
      * - indexOptionDefaults
        - array|object
        - Allows users to specify a default configuration for indexes when

source/whats-new.txt

@@ -49,6 +49,9 @@ improvements, and fixes:
   replaced by these new methods in a future driver release, so consider
   changing the usages in your application.
 
+- Deprecates the ``flags`` option, used for the deprecated MMAPv1 storage engine. 
+  This option will be removed in {+library-short+} v2.0.
+
 .. _php-lib-version-1.20:
 
 What's New in 1.20