Allow Temporary Workspaces to be disabled on a database

Customer requests DoltLab/DoltHub allow option to disable "Temporary Workspaces" for a database.

The customer's workflow is that each end user checks out a new branch, then makes `INSERT`s and `UPDATE`s via the DoltLab/DoltHub UI. Each branch is unique to each user. However, each write query creates a new Temporary Workspace that becomes cumbersome to manage, and is not very useful for this workflow.

There is also concern that a large number of Temporary Workspaces that have been created and are not removed add latency to the DoltLab/DoltHub UI.