feat: Support Grafana macros in SLS datasource

[guhanjie]

Summary

Implemented support for Grafana MySQL-style macros to simplify query writing for SLS datasource.

Changes

• Added pkg/macros.go: Implements InterpolateMacros function to parse and replace macros.
• Modified pkg/sls-plugin.go: Integrated macro interpolation into the QueryLogs flow.

Supported Macros

• $__time(__time__) -> to_unixtime(__time__) as time
• $__timeFilter(__time__) -> __time__ >= from AND __time__ < to
• $__timeGroup(__time__, '5m', [fill]) -> time_series(__time__, '5m', '%Y-%m-%d %H:%i:%s', fill)
• $__timeGroupAlias(__time__, '5m') -> time_series(...) as time

PS: __time__ is built-in time field in SLS log

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