Add a configuration item to change the expiration time for the RSS feed cache

[nexryai]

Description

Currently, the cache expiration time for RSS feeds appears to be hard-coded as 1 hour.

https://github.com/glanceapp/glance/blob/1512718d416f4580f7e7bb60c8d5878320e1f032/internal/glance/widget-rss.go#L43

I have a feed in my dashboard that should be updated frequently. It would be helpful to be able to set this to any time in the configuration

[ralphocdol]

There's a cache: config for almost everything, that's just a default if not set

https://github.com/glanceapp/glance/blob/233de7fc37da6976ac57c24e1607aa6e8dfd2fb7/internal/glance/widget.go#L253-L263

[nexryai]

I overlooked that config! Thank you for your kind reply.