refactor(cosmos-db): migrate to unified folder structure (Azure#37639)

* refactor the folder structure

* update cspell file

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Co-authored-by: Mike Harder <mharder@microsoft.com>
Co-authored-by: Qiaoqiao Zhang <55688292+qiaozha@users.noreply.github.com>

Author: 3 people

specification/cosmos-db/cspell.yaml

@@ -17,7 +17,7 @@ words:
   - gremlinrbac
   - undelete
 overrides:
-  - filename: '**/specification/cosmos-db/resource-manager/Microsoft.DocumentDB/**/*.json'
+  - filename: '**/specification/cosmos-db/resource-manager/Microsoft.DocumentDB/DocumentDB/**/*.json'
     words:
       - dotproduct
       - keyvaultkeyuri