gzip compressor: stop unnecessary re-compression when the chunk is already compressed

[daipom]

Is your feature request related to a problem? Please describe.

It appears the gzip compressor of out_s3 does unnecessary re-compression when the chunk is already compressed.

fluent-plugin-s3/lib/fluent/plugin/out_s3.rb

Lines 615 to 631 in 803cac2

	class GzipCompressor < Compressor
	def ext
	'gz'.freeze
	end
	def content_type
	'application/x-gzip'.freeze
	end
	def compress(chunk, tmp)
	w = Zlib::GzipWriter.new(tmp)
	chunk.write_to(w)
	w.finish
	ensure
	w.finish rescue nil
	end
	end

Describe the solution you'd like

The logic should be linked to Buffer settings, like out_file.

Describe alternatives you've considered

None.

Additional context

No response