DynamicFileCAContent and DynamicCertKeyPairContent used periodical job
to check whether the file content has changed, leading to 1 minute of
delay in worst case. This patch improves it by leveraging fsnotify
watcher. The content change will be reflected immediately.
Reload SNI certificate cert and key file from disk every minute and notify
the dynamic certificate controller when they change, allowing serving
tls config to be updated.
