We modify the requirements for using materialized views in tablet-based
keyspaces. Before, it was necessary to enable the configuration option
`rf_rack_valid_keyspaces`, having the cluster feature `VIEWS_WITH_TABLETS`
enabled, and using the experimental feature `views-with-tablets`.
We drop the last requirement.
We adjust code to that change and provide a new validation test.
We also update the user documentation to reflect the changes.
Fixesscylladb/scylladb#23030
(cherry picked from commit b409e85c20)
2bdf792f8e
