Deprecate the `/question/new` route for custom questions (#21558)

frontend/test/metabase-visual/notebook/notebook.cy.spec.js

...metabase/scenarios/admin/datamodel/hide_tables.cy.spec.js

...tabase/scenarios/binning/binning-reproductions.cy.spec.js

...t/metabase/scenarios/binning/qb-explicit-joins.cy.spec.js

frontend/test/metabase/scenarios/binning/sql.cy.spec.js

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...ions/14517-cc-do-not-remove-regex-escape-chars.cy.spec.js

frontend/test/metabase/scenarios/joins/joins-2.cy.spec.js

frontend/test/metabase/scenarios/joins/joins.cy.spec.js

.../reproductions/15342-mysql-correct-joins-order.cy.spec.js

...502-cannot-join-two-saved-questions-same-table.cy.spec.js

...ions-with-same-implicit-explicit-grouped-field.cy.spec.js

frontend/test/metabase/scenarios/models/models.cy.spec.js

...ive/reproductions/15946-mongo-pre-select-table.cy.spec.js

.../test/metabase/scenarios/permissions/sandboxes.cy.spec.js

frontend/test/metabase/scenarios/question/nested.cy.spec.js

frontend/test/metabase/scenarios/question/new.cy.spec.js

...tend/test/metabase/scenarios/question/notebook.cy.spec.js

...ctions/15714-cc-postgres-percentile-accepts-two-params.js

...tions/17963-mongo-filter-expression-compare-two-fields.js