fix(clients): fix expiry_interval unit error

[HJianBo]

1. The unit of expiry_interval was changed in 0704cbc in the previous implementation of 5.0, but the corresponding HTTP API returns were not changed accordingly. So we fixed it in this PR.
2. The unnecessary search parameter proto_name has been removed because all clients' proto_names must be MQTT, so this parameter is meaningless.

[id]

@HJianBo please rebase on latest master and address changelog conflict

[coveralls]

Pull Request Test Coverage Report for Build 3852146036

• 3 of 3 (100.0%) changed or added relevant lines in 1 file are covered.
• 19 unchanged lines in 8 files lost coverage.
• Overall coverage increased (+0.06%) to 79.817%

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Files with Coverage Reduction	New Missed Lines	%
apps/emqx_authz/src/emqx_authz_schema.erl	1	90.28%
apps/emqx_machine/src/emqx_machine.erl	1	79.31%
apps/emqx/src/bpapi/emqx_bpapi.erl	1	95.83%
apps/emqx/src/emqx_connection.erl	1	88.47%
apps/emqx/src/emqx_logger.erl	1	80.49%
apps/emqx/src/emqx_router_helper.erl	1	86.27%
apps/emqx/src/emqx_cm.erl	2	90.37%
apps/emqx/src/emqx_reason_codes.erl	11	89.71%

Totals
Change from base Build 3848746808:	0.06%
Covered Lines:	22736
Relevant Lines:	28485

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💛 - Coveralls