Update limits.mdx (#18964)

added max cache ttl time

Author: kathayl

src/content/docs/ai-gateway/reference/limits.mdx

@@ -12,6 +12,7 @@ The following limits apply to gateway configurations, logs, and related features
 | Feature                                                          | Limit                               |
 | ---------------------------------------------------------------- | ----------------------------------- |
 | [Cacheable request size](/ai-gateway/configuration/caching/)     | 25 MB per request                   |
+| [Cache TTL](/ai-gateway/configuration/caching/#cache-ttl-cf-aig-cache-ttl)     | 1 month               |
 | [Custom metadata](/ai-gateway/configuration/custom-metadata/)    | 5 entries per request               |
 | [Datasets](/ai-gateway/evaluations/set-up-evaluations/)          | 10 per gateway                      |
 | Gateways                                                         | 10 per account                      |