Somehow system."IndexInfo" table and column_family/built_indexes REST
API endpoint declare an index "built" at slightly different times:
The former a virtual table which declares an index completely built
when it appears on the system.built_views table.
The latter uses different data -- it takes the list of indexes in
the schema and eliminates indexes which are still listed in the
system.scylla_views_builds_in_progress table.
The mentioned system. tables are updated at different times, so API
notices the change a bit later. It's worth improving the consistency
of these two APIs by making the REST API endpoint piggy-back the
load_built_views() instead of load_view_build_progress(). With that
change the filtering of indexes should be negated.
Fixes#21587
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>