Extend Storage support to relative local FS paths

[gruuya]

Closes #711.

Add support for relative paths in local FS storage, keeping the rest of the functionality intact. An example how this can be helpful can be seen here https://github.com/splitgraph/seafowl/pull/744/files.

[Fokko]

Hey @gruuya Thanks for creating this PR. Unfortunately, Iceberg does not support relative paths. There is a long open issue apache/iceberg#1617 but it is pretty complex to implement. As an example, merge-on-read uses absolute paths to know which files to apply the deletes to. Adding support for relative paths makes this very brittle since the path might not be matched correctly, resulting in data correctness issues.

Instead, for testing, I would suggest symlinking similar to what I did in pola-rs/polars#10375 or running a MinIO S3 container, similar to the integration tests of iceberg-rust itself: https://github.com/apache/iceberg-rust/blob/main/crates/catalog/rest/testdata/rest_catalog/docker-compose.yaml

[gruuya]

Oh I see, didn't realize it was prohibited at the spec level. Thanks, closing.

[Fokko]

@gruuya No worries, thanks for your understanding.