Improve documentation of table ID

We can make it clear that the table ID is not editable, and if you changed it the system would attempt to create a new table. That would fail because there's already a table with the same name.

Locate the existing documentation for table IDs and read how editability is currently described. Clarify that the table ID cannot be edited, and explain that changing it would attempt to create a new table with the same name and fail because that table already exists.

Written by the indexing model from the issue text.