Enhancement: Add support for a config file in iceberg-rust

[s-akhtar-baig]

As a follow-up to https://github.com/apache/iceberg-rust/pull/374,

• Implement a config file for iceberg-rust
• Provide users with an additional option to set legacy-current-snapshot-id as a configuration value

[liurenjie1024]

I think to fix #374, we should decouple two things:

1. Add a setting in metadata reader/writer to deal with current-snapshot-id
2. How to enable the setting, either through env or config file.

If we actually want a config file, we should discuss the format actually.