T6712: Add nonproduction banner (backport #4148)

[mergify]

Change Summary

Add nonproduction banner

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, renaming)
• Refactoring (no functional changes)
• Migration from an old Vyatta component to vyos-1x, please link to related PR inside obsoleted component
• Other (please describe): Add nonproduction banner

Related Task(s)

• https://vyos.dev/T6712

Related PR(s)

Component(s) name

banner

Proposed changes

How to test

vyos@eve-r1# set system login banner post-login "Hello, VyOS!"
[edit]
vyos@eve-r1# commit
[edit]
vyos@eve-r1# exit
Warning: configuration changes have not been saved.
exit
vyos@eve-r1:~$ exit
logout

Welcome to VyOS - eve-r1 ttyS0

eve-r1 login: vyos
Password:
Hello, VyOS!

---
Warning: This VyOS system is not a stable long-term support version and is not intended for production use.
vyos@eve-r1:~$

Smoketest result

Checklist:

• I have read the CONTRIBUTING document
• I have linked this PR to one or more Phabricator Task(s)
• I have run the components SMOKETESTS if applicable
• My commit headlines contain a valid Task id
• My change requires a change to the documentation
• I have updated the documentation accordingly

---

This is an automatic backport of pull request #4148 done by [Mergify](https://mergify.com).

[github-actions]

👍
No issues in PR Title / Commit Title

[github-actions]

✅ No issues found in unused-imports check.. Please refer the workflow run

[github-actions]

CI integration 👍 passed!

Details

CI logs

• CLI Smoketests (no interfaces) 👍 passed
• CLI Smoketests (interfaces only) 👍 passed
• Config tests 👍 passed
• RAID1 tests 👍 passed
• TPM tests 👍 passed