Extract "custom column" into a separate e2e and CI group (#18336)

* Extract cc reproductions from `question` group

* Extract custom-column spec

* Extract custom column help-text spec

* Extract custom column typing-suggestion spec

* Extract custom column error-feedback spec

* Expand typing-suggestions spec

* Consolidate repros

* Extract custom column data-type spec

* Remove references to `cy.server` from custom-column spec

* Extract custom column expression-editor spec

* Remove duplicate tests

* Extract and unskip repro for #13289

* Register custom column helpers

* Use CC helper in tests

* Move related tests to help-text spec

* Enable "custom-column" e2e group in CI

* Delete a duplicate repro for #13289

* Remove obsolete test

* Expand error-feedback spec

* Extract and expand repro for #14843

* Fix linter errors