Enable long-running operations to run in the background

It would be useful to be able to run potentially long-running operations such as create_distributed_table, CREATE INDEX, and rebalance_table_shards in the background such that the user does not need to keep a terminal window open. The status/progress and result of the command need to be made visible in a table.

This functionality is somewhat similar to pg_cron, but pg_cron only supports periodically running a command.

Start by examining how create_distributed_table, CREATE INDEX, and rebalance_table_shards currently run, then compare the requested behavior with pg_cron. Done means long-running operations can continue after the terminal closes, with their status, progress, and result visible in a table.

Written by the indexing model from the issue text.