chore: persist template import terraform plan in postgres (#17012)

coderd/database/migrations/000306_template_version_terraform_values.up.sql

@@ -0,0 +1,5 @@
+create table template_version_terraform_values (
+	template_version_id uuid not null unique references template_versions(id) on delete cascade,
+	updated_at timestamptz not null default now(),
+	cached_plan jsonb not null
+);