add missing atlas search extract (#855)

Author: jeff-allen-mongo

source/includes/extracts-atlas-search-facts.yaml

@@ -0,0 +1,27 @@
+ref: fact-text-search-legacy-atlas
+content: |
+
+  MongoDB offers a :atlas:`full-text search solution, MongoDB Atlas 
+  Search </atlas-search/>`, for data hosted on :atlas:`MongoDB 
+  Atlas </>`. A legacy text search capability is available for users 
+  self-managing MongoDB deployments. 
+
+---
+ref: fact-regex-search-legacy-atlas
+content: |
+
+  **For data hosted on MongoDB Atlas**, MongoDB offers a 
+  full-text search solution, :atlas:`MongoDB Atlas Search 
+  </atlas-search/>`. If you frequently run case-insensitive regex 
+  queries (utilizing the ``i`` option), MongoDB recommends Atlas Search 
+  queries that use the :pipeline:`$search` aggregation pipeline stage. 
+  
+  :atlas:`Atlas Search queries </reference/atlas-search/searching/>` 
+  significiantly improve the performance of text queries and offer more 
+  options for customizing query parameters. To learn more, see 
+  :atlas:`MongoDB Atlas Search </atlas-search/>`. 
+  
+  **For self-managed deployments**, you can find information on our 
+  regex capability below.
+
+...