feat(coderd/database): add template_usage_stats table and rollup query (#12664)

Add `template_usage_stats` table for aggregating tempalte usage data.
Data is rolled up by the `UpsertTemplateUsageStats` query, which fetches
data from the `workspace_agent_stats` and `workspace_app_stats` tables.

coderd/database/migrations/testdata/fixtures/000203_template_usage_stats.up.sql

@@ -0,0 +1,30 @@
+INSERT INTO
+	template_usage_stats (
+		start_time,
+		end_time,
+		template_id,
+		user_id,
+		median_latency_ms,
+		usage_mins,
+		ssh_mins,
+		sftp_mins,
+		reconnecting_pty_mins,
+		vscode_mins,
+		jetbrains_mins,
+		app_usage_mins
+	)
+VALUES
+	(
+		date_trunc('hour', NOW()),
+		date_trunc('hour', NOW()) + '30 minute'::interval,
+		gen_random_uuid(),
+		gen_random_uuid(),
+		45.342::real,
+		30, -- usage
+		30, -- ssh
+		5, -- sftp
+		2, -- reconnecting_pty
+		10, -- vscode
+		10, -- jetbrains
+		'{"[terminal]": 2, "code-server": 30}'::jsonb
+	);