pinot-admin.sh inconsistent behavior when updating table config using AddTable

Realtime table config could be updated using pinot-admin.sh but not offline table config
updating offline table config using pinot-admin.sh AddTable throws table already exists error.

Start with pinot-admin.sh and the AddTable path, comparing how realtime and offline table configuration updates are handled. Reproduce the offline update and verify that it updates an existing table configuration without raising a table-already-exists error.

Written by the indexing model from the issue text.