Fix #237: Add Prefix to File Chunks

[gugacavalieri]

Fixes #237.

This PR adds trailing zeros when storing the dump chunks. This is done in order to keep the correct file order when restoring dumps. Instead of outputting 1.dump the code now outputs 0001.dump.

Using 4 digits will allow a max of 9999 chunk parts. With a chunk_size of 100MB this allow dumps to have a max of 1TB in the correct order.

The issue is described here: https://github.com/Qovery/Replibyte/issues/237