The new role version splits backup_borg_location_exclude_patterns into
auto/custom components, following the existing split for
backup_borg_location_source_directories. The playbook now wires its
computed values into the _auto variables for both, so users can append
their own entries via the _custom variables instead of redefining the
whole lists and accidentally dropping playbook-provided values.
Previously, redefining backup_borg_location_exclude_patterns dropped
the postgres_data_path exclusion (making borg walk live Postgres data
and fail with warning exit codes), and the playbook's own
source_directories wiring made the role's _custom variable a no-op.

Related to #5092

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>