NTP authentication: SHA1-128 and SHA2-256

This feature adds support for SHA1-128 and SHA2-256 authentication for NTP. NTP authentication uses a shared key to verify trusted time sources before synchronizing the system clock, helping protect time synchronization from unauthorized or spoofed NTP messages. To configure NTP authentication, define an authentication key under the [edit system ntp] hierarchy and specify the desired SHA-based authentication type and key value. For example, SHA1-128 authentication can be configured using the 'authentication-key' statement with type 'sha1'.