Frontend work for adding multi-column unique constraints

[kgodey]

Problem

Users may want to create unique constraints on tables.

Proposed solution

We should provide a way to create unique constraints from the UI following the "Working with Columns" design spec.

This covers allowing the addition of a new unique constraint, including auto-complete for column names.

Adding other types of constraints will not yet be supported.

Additional context

• Design issue: Design for editing column properties and table constraints #324
• Design discussion: Working with Columns #436
• Backend issue: CRUD API for table constraints #326
• Backend PR: API for adding and removing table constraints #488
• Blocking frontend issue: Frontend work for viewing and deleting table constraints #328

[github-actions]

This issue has not been updated in 90 days and is being marked as stale.

[kgodey]

This is ready for work now that #328 is done.

[seancolsen]

@ghislaineguerin and I chatted about the design for this and agreed on the following:

• Build on the current Table Constraints modal.
• Insert an "Add" button above the list of constraints.
• When you click "Add", the whole contents of the modal slide to the left and are replaced by a form to add a new table constraint.
  • The form has "Cancel" and "Save" buttons at the bottom.
  • If you click "Cancel", the modal slides back to view the list of constraints.
  • If you fill out the form and click "Add", the modal slides back to view the list of constraints and the newly-added constraint is briefly highlighted.