chore: convert agent stats to use a table (#6374)

* chore: convert workspace agent stats from json to table

* chore: convert agent stats to use a table

Backwards compatibility becomes hard when all agent stats are in a JSON blob.
We also want to query this table for new agents that are failing health checks
so we can display it in the UI.

* Fix migration using default values

coderd/database/queries/workspaceagentstats.sql

@@ -0,0 +1,45 @@
+-- name: InsertWorkspaceAgentStat :one
+INSERT INTO
+	workspace_agent_stats (
+		id,
+		created_at,
+		user_id,
+		workspace_id,
+		template_id,
+		agent_id,
+		connections_by_proto,
+		connection_count,
+		rx_packets,
+		rx_bytes,
+		tx_packets,
+		tx_bytes
+	)
+VALUES
+	($1, $2, $3, $4, $5, $6, $7, $8, $9, $10, $11, $12) RETURNING *;
+
+-- name: GetTemplateDAUs :many
+SELECT
+	(created_at at TIME ZONE 'UTC')::date as date,
+	user_id
+FROM
+	workspace_agent_stats
+WHERE
+	template_id = $1
+GROUP BY
+	date, user_id
+ORDER BY
+	date ASC;
+
+-- name: GetDeploymentDAUs :many
+SELECT
+	(created_at at TIME ZONE 'UTC')::date as date,
+	user_id
+FROM
+	workspace_agent_stats
+GROUP BY
+	date, user_id
+ORDER BY
+	date ASC;
+
+-- name: DeleteOldWorkspaceAgentStats :exec
+DELETE FROM workspace_agent_stats WHERE created_at < NOW() - INTERVAL '30 days';