Move SnapshotConfig into its own module (#18331)

Also move ArchiveFormat to snapshot_utils, and do not
reexport SnapshotVersion.

runtime/src/lib.rs

@@ -33,6 +33,7 @@ mod read_only_accounts_cache;
 pub mod rent_collector;
 pub mod secondary_index;
 pub mod serde_snapshot;
+pub mod snapshot_config;
 pub mod snapshot_package;
 pub mod snapshot_runtime_info;
 pub mod snapshot_utils;