syslog: T4251: Rename "permitted-peers" to "permitted-peer" and improve TLS checks

[alexandr-san4ez]

Change summary

• Renamed permitted-peers to permitted-peer across templates, schema, and tests.
• Added support for multiple permitted-peer entries and trimmed empty values.
• Replaced TLS/UDP warning with ConfigError for strict validation.
• Updated tests to use TCP for TLS and verified new validation logic.

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):

Related Task(s)

• https://vyos.dev/T4251

Related PR(s)

• syslog: T4251: Add TLS support to syslog #4734
• syslog: T4251: Rename "permitted-peers" to "permitted-peer" vyos-documentation#1701

How to test / Smoketest result

$ /usr/libexec/vyos/tests/smoke/cli/test_system_syslog.py
test_basic (__main__.TestRSYSLOGService.test_basic) ... ok
test_console (__main__.TestRSYSLOGService.test_console) ... ok
test_remote (__main__.TestRSYSLOGService.test_remote) ... ok
test_remote_tls (__main__.TestRSYSLOGService.test_remote_tls) ... ok
test_remote_tls_protocol_udp (__main__.TestRSYSLOGService.test_remote_tls_protocol_udp) ... ok
test_vrf_source_address (__main__.TestRSYSLOGService.test_vrf_source_address) ... ok

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

[github-actions]

👍
No issues in PR Title / Commit Title

[github-actions]

CI integration 👍 passed!

Details

CI logs

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