feat(anta): Added the test case to verify NTP associations functionality

[vitthalmagadum]

Description

NTP associations for all NTP servers should be up as denoted by the "condition" field below, and the primary NTP server should be preferred.

primary server will have condition "sys.peer", and pri server is denoted using "preferred: true " other servers will have condition "candidate"

Fixes #753

Checklist:

• [X] My code follows the style guidelines of this project
• [X] I have performed a self-review of my code
• [X] I have run pre-commit for code linting and typing (pre-commit run)
• [ ] I have made corresponding changes to the documentation
• [ ] I have added tests that prove my fix is effective or that my feature works
• [X] New and existing unit tests pass locally with my changes (tox -e testenv)