Add comments to getCleanCacheGracePeriodSeconds in fluid/pkg/ddc/alluxio/cache.go

[Dingzhen230]

Which function do you want to add comments to?
getCleanCacheGracePeriodSeconds in fluid/pkg/ddc/alluxio/cache.go
What comments do you want to add?

// getCleanCacheGracePeriodSeconds retrieves the grace period in seconds for cleaning the cache.
// It first attempts to get the runtime configuration. If successful, it checks if the grace period
// is specified in the runtime's CleanCachePolicy. If specified, it returns that value. Otherwise,
// it returns a default value.