* s3tables: answer 404 for a table name that was renamed away
A rename leaves the source directory in place to hold the data under
it, with its catalog attributes cleared. UpdateTable, DeleteTable, the
table policy calls and the table maintenance calls read the metadata
attribute of that directory and reported its absence as an internal
error, so they answered 500, and GetTablePolicy answered NoSuchPolicy.
An absent metadata attribute now reads as a missing entry. tableMetadata
reports it as both filer_pb.ErrNotFound and the attribute error, so
callers that test for either keep working. The policy and maintenance
handlers read the attribute through the new readTableMetadataAttr, which
reports filer_pb.ErrNotFound, so each call answers NoSuchTable.
* s3tables: a view record without its metadata reads absent too
* s3tables: refuse a catalog write that lands on a metadata-less record
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Co-authored-by: user.email <chrislusf@users.noreply.github.com>
