input: send resume signal to the input thread event loop if plugin is threaded

[danlenar]

Fixes #7071

I was getting the following error.

[2023/08/09 06:48:50] [ warn] [input] tail.0 paused (mem buf overlimit)
[2023/08/09 06:48:50] [ info] [input] tail.0 resume (mem buf overlimit)
[2023/08/09 06:48:50] [ warn] [input] tail.0 paused (mem buf overlimit)
[2023/08/09 06:48:50] [error] [input] cannot resume collector tail.0:2, already running

Log processing would start going to standstill once the "cannot resume collector" line was logged.
After looking at the code, I found a race condition around pause/resume.

flb_input_pause sends a signal to input thread event loop
https://github.com/fluent/fluent-bit/blob/v2.1.8/src/flb_input.c#L1673

flb_input_resume is done by the main thread instead of sending signal to input thread event loop
https://github.com/fluent/fluent-bit/blob/v2.1.8/src/flb_input.c#L1695

The fix is to have flb_input_resume also send signal to the input thread, so pause and resume don't happen out of order or stomp on each other.

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[leonardo-albertovich]

@edsiper, this PR looks good to me and I think we should prioritize it.

Thanks a lot for taking the time to address this issue @danlenar!