chore(auth_http): add changelog

Co-authored-by: Thales Macedo Garitezi <thalesmg@gmail.com>

changes/ce/fix-13040.en.md

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+Improve HTTP authentication
+
+* Emit more meaningful error log message for unknown/missing HTTP content-type header.
+* Fix double encoding of query params in authentication HTTP requests.
+* Emit meaningful error message if POST method and JSON content type are configured for
+authentication HTTP request but JSON template cannot be rendered into a valid JSON. E.g.
+when a template contains `${password}` placeholder, but a client passed non-utf8 password.