Better session isolation for Workbench UI tabs

In the Workbench UI, connections/sessions to a Hosted Dolt database are currently pooled at the database/branch level. This means if you have multiple tabs open with the Workbench UI for the same branch of the same database, session data set in one Workbench will sometimes be visible in the second Workbench tab (depending on which connection gets pulled from the pool). Making this web UI work in a stateful way with the same session behavior as a SQL client is tricky, but would be nice to improve on.