Updating collect-timeout will not change scrape_timeout configuration

[dashmage]

The scrape_timeout for Prometheus is set as part of the charm's init method when instantiating the CosAgentProvider class. This value is obtained from the charm's collect-timeout config.

But the problem is that once the charm is running and the user changes the value of collect-timeout, this will not change the scrape_timeout value again since the charm's init method won't be called. So Prometheus will always be configured with the default collect-timeout value of 10s.

[dashmage]

Since we're updating the relation data when config change event occurs (due to the refresh_events configuration), it would look like the scrape_timeout would also be updated along with that.

This would require some manual verification to be 100% certain. Maybe we could have a new test for this as part of the COS integration tests?