Pass S3 endpoint and keys as helper container env vars and run mc alias
via those variables so the stored import command no longer contains
access keys or secrets. Start the helper in a separate remote process,
use the storage filesystem adapter for object checks, and remove a
credential temp file during import cleanup when the path is safe.
Hold a cache lock keyed by database UUID across the active-import
check and remote_process so two concurrent requests cannot both
queue a restore against the same database.
Allow single-database PostgreSQL imports to drop matching objects before restore. The API and import form accept replace_existing, which adds --clean --if-exists to pg_restore, and pg_restore now uses --exit-on-error.
Andras Bacsai