system_config: add path attribute in system/log section

[Watson1978]

This feature was introduced at https://github.com/fluent/fluentd/pull/4604

[daipom]

Thanks!

It appears that we need to fix other areas.

For example: https://docs.fluentd.org/deployment/logging#output-to-log-file

It would be a bit difficult for users to understand this feature because it can also be set by command line options. rotate_age and rotate_size are the same, so the descriptions of them might be helpful.

[Watson1978]

Thank you for your review.

OK, I will add more content in Logging page.

[Watson1978]

I added the description in logging page.

[kenhys]

Merge when v1.18 was released.

[daipom]

Thanks for this update!