db: degrade view building progress loading error to warning
db: degrade view building progress loading error to warning

When the view builder cannot read view building progress from an
internal CQL table it produces an error message, but that only confuses
the user and the test suite -- this situation is entirely recoverable,
because the builder simply assumes that there is no progress and the
view building should start from scratch.

Fixes #7527

Closes #7558

scylladb/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla