Add commit-ready functional tests under tests/junipernetworks.junos

[Brij812]

This pull request introduces a comprehensive set of functional tests for the Juniper Ansible Collection for Junos (junipernetworks.junos).

Key additions:

• 37 commit-ready functional test playbooks located under tests/junipernetworks.junos/
• All playbooks follow official module documentation examples and include states like merged, replaced, overridden, deleted, gathered, rendered, and parsed
• Clean inventory and ansible.cfg files prepared for netconf, local, and network_cli connection types
• run_all_tests.sh script to execute all test cases in sequence
• A detailed README.md with execution instructions

All sensitive values (e.g., IPs, usernames, passwords) have been masked with placeholders (xx.xx.xx.xx) to make the tests reusable and commit-safe.