Authn: backword compatibility for 4.x authn data

[HJianBo]

• feat(authn-redis): needs to compatible with 4.x auth data
• fix(authn): correct peerhost placeholder rendering

[coveralls]

Pull Request Test Coverage Report for Build 2593905632

• 14 of 15 (93.33%) changed or added relevant lines in 2 files are covered.
• 61 unchanged lines in 18 files lost coverage.
• Overall coverage increased (+0.002%) to 79.072%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
apps/emqx_authn/src/emqx_authn_utils.erl	8	9	88.89%

Files with Coverage Reduction	New Missed Lines	%
apps/emqx_authz/src/emqx_authz_schema.erl	1	90.28%
apps/emqx_dashboard/src/emqx_dashboard_monitor.erl	1	69.93%
apps/emqx_machine/src/emqx_machine.erl	1	79.31%
apps/emqx_slow_subs/src/emqx_slow_subs.erl	1	77.42%
apps/emqx/src/emqx_channel.erl	1	85.85%
apps/emqx/src/emqx_cm.erl	1	89.45%
apps/emqx/src/emqx_config.erl	1	84.69%
apps/emqx/src/emqx_flapping.erl	1	85.11%
apps/emqx/src/emqx_frame.erl	1	88.41%
apps/emqx/src/emqx_router_utils.erl	1	58.14%

Totals
Change from base Build 2584967010:	0.002%
Covered Lines:	20762
Relevant Lines:	26257

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💛 - Coveralls