Sync synchronises the cluster to the files in a directory.

These are all the types of events.

这个变量保存需要被替换的ssh地址.

Commit represents the commit information in a sync event.

SyncEventMetadata is the metadata for when new a commit is synced to the cluster.

EventMetadata is a type safety trick used to make sure that Metadata field of Event is always a pointer, so that consumers can cast without being concerned about encountering a value type instead.