Update ops dashboard and alert manager examples to show license expiry details

[hcoyote]

As of 24.2.10, we now have the following metric to show seconds to expiry.

# HELP redpanda_cluster_features_enterprise_license_expiry_sec Number of seconds remaining until the Enterprise license expires
# TYPE redpanda_cluster_features_enterprise_license_expiry_sec gauge
redpanda_cluster_features_enterprise_license_expiry_sec{} -1.000000

We should add a dashboard widget showing days left to expiration, and allow for an alert manager that fires off when within say, 4 weeks, 2 weeks, 1 week, 1 day alerting.