feat: add sysmon config handler to reload conf

[zhongwencool]

No description provided.

[codeball-ai-writer]

Codeball: LGTM! 👍 dashboard

[coveralls]

Pull Request Test Coverage Report for Build 2709337523

• 28 of 31 (90.32%) changed or added relevant lines in 3 files are covered.
• 31 unchanged lines in 15 files lost coverage.
• Overall coverage decreased (-0.02%) to 78.818%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
apps/emqx/src/emqx_os_mon.erl	6	9	66.67%

Files with Coverage Reduction	New Missed Lines	%
apps/emqx_bridge/src/emqx_bridge.erl	1	85.11%
apps/emqx_dashboard/src/emqx_dashboard_monitor.erl	1	69.93%
apps/emqx_gateway/src/mqttsn/emqx_sn_channel.erl	1	72.92%
apps/emqx/src/emqx_authentication_config.erl	1	84.75%
apps/emqx/src/emqx_config.erl	1	84.83%
apps/emqx/src/emqx_config_handler.erl	1	96.34%
apps/emqx/src/emqx_connection.erl	1	84.99%
apps/emqx/src/emqx_flapping.erl	1	85.11%
apps/emqx/src/emqx_logger.erl	1	80.49%
apps/emqx/src/emqx_logger_textfmt.erl	1	47.37%

Totals
Change from base Build 2708675048:	-0.02%
Covered Lines:	20826
Relevant Lines:	26423

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💛 - Coveralls