Feature request: support to update snapshot summary

[dentiny]

Is your feature request related to a problem or challenge?

Context: I would like to set some self-defined metadata (pretty small, less than 100 bytes) for a particular snapshot in the current snapshot.

Search around the code, I think the best place to store might be snapshot summary.

iceberg-rust/crates/iceberg/src/spec/snapshot.rs

Line 74 in f9061cc

/// Other summary data.

Interface-wise I imagine something similar to pyiceberg:

• We expose set_properties and get_properties interface for Transaction

Describe the solution you'd like

There're a lot of bad workarounds (i.e. store the metadata into puffin files, hack the TableMetadata, etc), but I would expect the summary update operation to be exposed at transaction layer.

Willingness to contribute

I can contribute to this feature independently

[dentiny]

It's worth noting, existing interfaces only allow to modify table properties, but it's completely different from snapshot properties, and not expected to embed arbitrary metadata:

iceberg-rust/crates/iceberg/src/spec/table_metadata.rs

Lines 135 to 138 in f9061cc

	///A string to string map of table properties. This is used to control settings that
	/// affect reading and writing and is not intended to be used for arbitrary metadata.
	/// For example, commit.retry.num-retries is used to control the number of commit retries.
	pub(crate) properties: HashMap<String, String>,