feat: use JWT ticket to avoid DB queries on apps (#6148)

Issue a JWT ticket on the first request with a short expiry that
contains details about which workspace/agent/app combo the ticket is
valid for.

coderd/database/queries/siteconfig.sql

@@ -30,3 +30,9 @@ ON CONFLICT (key) DO UPDATE SET value = $1 WHERE site_configs.key = 'logo_url';
 
 -- name: GetLogoURL :one
 SELECT value FROM site_configs WHERE key = 'logo_url';
+
+-- name: GetAppSigningKey :one
+SELECT value FROM site_configs WHERE key = 'app_signing_key';
+
+-- name: InsertAppSigningKey :exec
+INSERT INTO site_configs (key, value) VALUES ('app_signing_key', $1);