feat: add timezone_to_second/1 function to rule engine

[kjellwinblad]

This commit adds the functions timezone_to_offset_seconds and its alias timezone_to_second to the rule engine. As the names suggests, these functions convert a timzone offset string such as "+02:00", "Z", "local" to an integer representing how many seconds that the given timezone differs from UTC. timezone_to_offset_seconds is the one of the two functions that should be advertised while timezone_to_second in kept for backwards compatibility with 4.X.

Fixes:
https://emqx.atlassian.net/browse/EMQX-10058

Summary

🤖 Generated by Copilot at 995025b

Added timezone conversion functions and tests to emqx_rule_funcs and updated emqx_machine version.

PR Checklist

Please convert it to a draft if any of the following conditions are not met. Reviewers may skip over until all the items are checked:

• Added tests for the changes
• Changed lines covered in coverage report
• Change log has been added to changes/{ce,ee}/(feat|perf|fix)-<PR-id>.en.md files
• For internal contributor: there is a jira ticket to track this change
• If there should be document changes, a PR to emqx-docs.git is sent, or a jira ticket is created to follow up
• Schema changes are backward compatible

[kjellwinblad]

Sorry, the test suite was broken but has been fixed by this commit (354603d) so I need another approval.

[coveralls]

Pull Request Test Coverage Report for Build 5113281055

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• 34 unchanged lines in 12 files lost coverage.
• Overall coverage increased (+0.007%) to 81.622%

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Files with Coverage Reduction	New Missed Lines	%
apps/emqx_management/src/emqx_mgmt_util.erl	1	13.79%
apps/emqx_modules/src/emqx_delayed.erl	1	95.65%
apps/emqx/src/emqx_cm.erl	1	91.6%
apps/emqx/src/emqx_config_handler.erl	1	96.25%
apps/emqx/src/emqx_logger_textfmt.erl	1	59.09%
apps/emqx/src/emqx_session.erl	1	87.25%
apps/emqx_resource/src/emqx_resource_buffer_worker.erl	2	93.09%
apps/emqx/src/emqx_broker.erl	2	87.64%
apps/emqx/src/emqx_channel.erl	2	87.69%
apps/emqx_gateway_exproto/src/emqx_exproto_gcli.erl	3	48.78%

Totals
Change from base Build 5111811576:	0.007%
Covered Lines:	28656
Relevant Lines:	35108

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💛 - Coveralls

[yanzhiemq]

Enhancements

• A new utility function timezone_to_offset_seconds/1 has been added to the rule engine SQL language. This function converts a timezone string (for example, "+02:00", "Z" and "local") to the corresponding offset in seconds.

[yanzhiemq]

增强

• 规则引擎 SQL 语言新增了一个实用函数 timezone_to_offset_seconds/1。该函数将时区字符串（例如"+02:00"、"Z"和"local"）转换为相应的偏移秒数。