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

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

@@ -0,0 +1 @@
+drop table template_version_terraform_values;

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

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+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
+);

coderd/database/migrations/testdata/fixtures/000306_add_terraform_plans.up.sql

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+insert into
+	template_version_terraform_values (
+		template_version_id,
+		cached_plan,
+		updated_at
+	)
+	select
+		id,
+		'{}',
+		now()
+	from
+		template_versions;