Not setting gcs chunk_size option overwrites library default

[devoxel]

The default is 16MiB, and when you set Writer.ChunkSize to 0, GCS will disable disable chunking, not use the default.

Because the clickhouse-backup library uses the zero value from a yaml config, rather than not setting, it will remove completely the chunking feature by default.

This feels probably unintentional & undesirable, as it will fully disable transient error retries on the GCS side (which appears to be bugged also, see #1291).

For large files, it also increases the chances of hitting these transient errors, because files may take a long time to upload. We consistently observed GOAWAYs on these streams during the duration of the file upload.

[Slach]

let's make default value in config.go in this case

[Slach]

thanks a lot for repoting