plugin_proxy: core: expose more callbacks for golang plugins

[cosmo0920]

To support hot-reloading with Golang plugins which built on top of calyptia/plugin library, we need to expose more callbacks into Golang interface.

• Exposure of pre_run callbacks need to ensure only once execution before running with input callback or flush callback
• Exposure of pre_register callback needs to ensure initialization for waitgroup values before executing register callbacks
• Expose pause/resume callbacks to synchronize the statuses of input plugins against the lifecycle of fluent-bit itself

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Testing
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• Example configuration file for the change
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• Run local packaging test showing all targets (including any new ones) build.
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Documentation

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Backporting

• Backport to latest stable release.

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