Add an obs client configurer WithBuffersSize

[Turkish]

Add a configurer WithBuffersSize to allow changing the default size of the httpClient buffers.
Currently the only way would be to recreate the full http.Transport and pass it to the WithHttpTransport configurer.
But this means loosing the internal implementation already done by the SDK, like tls config, or timeouts.

// WithBuffersSize is a configurer for ObsClient to set the customized ReadBufferSize and WriteBufferSize.
func WithBuffersSize(readBufferSize, writeBufferSize int) configurer {
	return func(conf *config) {
		conf.readBufferSize = readBufferSize
		conf.writeBufferSize = writeBufferSize
	}
}