doc: added missing topic "charging_state" in mqtt doc #558

Job	Run time
check_paths / check_paths	5s
spell_check / Spell check	5s
ensure_linting / check_linting	4m 51s
elixir_dep_verification_and_static_analysis / Verify dependencies, POT files, unused dependencies, static analysis	1m 21s
elixir_test / Test	1m 17s
	7m 39s

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