refactor(coderd): drop sidebar app constraint and simplify provisionerdserver for tasks (#20591)

Updates coder/internal#973
Updates coder/internal#974

coderd/database/migrations/000394_drop_workspace_build_ai_task_sidebar_app_id_required.down.sql

@@ -0,0 +1,4 @@
+-- WARNING: Restoring this constraint after running a newer version of coderd
+-- and using tasks is bound to break this constraint.
+ALTER TABLE workspace_builds
+ADD CONSTRAINT workspace_builds_ai_task_sidebar_app_id_required CHECK (((((has_ai_task IS NULL) OR (has_ai_task = false)) AND (ai_task_sidebar_app_id IS NULL)) OR ((has_ai_task = true) AND (ai_task_sidebar_app_id IS NOT NULL))));

coderd/database/migrations/000394_drop_workspace_build_ai_task_sidebar_app_id_required.up.sql

@@ -0,0 +1,4 @@
+-- We no longer need to enforce this constraint as tasks have their own data
+-- model.
+ALTER TABLE workspace_builds
+DROP CONSTRAINT workspace_builds_ai_task_sidebar_app_id_required;