Add reason field for workspace builds (#2438)

* add reason field for workspace build

* add the reason field to FE via API

* update BuildReasonMember to BuildReasonInitiator

* add unit tests

* add more unit tests

* add error for unknown transition

* fix lint

* add documentation

* fix unit tests

* fix generated types

* remove nested transaction

* rename migration file

coderd/database/migrations/000025_workspace_build_reason.down.sql

@@ -0,0 +1,4 @@
+ALTER TABLE ONLY workspace_builds
+    DROP COLUMN IF EXISTS reason;
+
+DROP TYPE build_reason;

coderd/database/migrations/000025_workspace_build_reason.up.sql

@@ -0,0 +1,4 @@
+CREATE TYPE build_reason AS ENUM ('initiator', 'autostart', 'autostop');
+
+ALTER TABLE ONLY workspace_builds
+    ADD COLUMN IF NOT EXISTS reason build_reason NOT NULL DEFAULT 'initiator';