adding TOC entry for full-text search (dotnet#5029)

Author: maumar

entity-framework/toc.yml

@@ -440,6 +440,8 @@
           href: core/providers/cosmos/unstructured-data.md
         - name: Vector search
           href: core/providers/cosmos/vector-search.md
+        - name: Full text search
+          href: core/providers/cosmos/full-text-search.md
         - name: Azure Cosmos DB limitations
           href: core/providers/cosmos/limitations.md
         - name: End-to-end sample