Protection against "upgrading" a repository

[paraseba]

We expect repositories to live much longer than a single Icechunk version. As such, it's expected that a repository will have a mix of files generated with different versions of the spec.

Icechunk guarantees backwards compatibility, newer versions will be able to read repos written with previous versions (up to some limit potentially)

Icechunk does not promise that users will be able to read with older Icechunk versions, repos written with newer versions.

So it's easy to mistakenly do a small write to a Repository, with a new version, and invalidate the repo for all other users that are using a previous version.

There should be some protection against this, for example:

• require some form of confirmation before writing to a repo with a newer spec version
• require a manual step before allowing the upgrade
• emit a warning (this sounds too weak)