DOCS-10757 Add page for error codes (#5319) (#6547)

* DOCS-10757 Add page for error codes (#5319)

* add error code page and update TOC

* removed obsolute and not-yet-available

* resolve git merge conflict tags

Author: MongoCaleb

source/reference.txt

@@ -30,6 +30,9 @@ Reference
    Documentation of :binary:`~bin.mongod` and :binary:`~bin.mongos`
    and all other tools distributed with MongoDB.
 
+:ref:`server-error-codes`
+   Details the error codes that MongoDB returns.
+
 :doc:`/reference/configuration-options`
    Full documentation of the configuration file and available
    run-time operations.
@@ -101,6 +104,7 @@ Reference
    /reference/configuration-options
    /reference/parameters
    /reference/limits
+   /reference/error-codes
    /reference/explain-results
    /reference/system-collections
    /reference/connection-string