Previously, LSI keys were stored as separate, top-level columns in the base table. This patch changes this behavior for newly created tables, so that the key columns are stored inside the `:attrs` map. Then, we use top-level computed columns instead of regular ones.
This makes LSI storage consistent with GSIs and allows the use of a collection tombstone on `:attrs` to delete all attributes in a row except for keys in new tables.
Refs https://github.com/scylladb/scylladb/pull/24991
Refs https://github.com/scylladb/scylladb/issues/6930Closesscylladb/scylladb#25796
* github.com:scylladb/scylladb:
alternator: Store LSI keys in :attrs for newly created tables
alternator/test: Add LSI tests based mostly on the existing GSI tests
7be5454db1