This change introduces a validation script to ensure that DNS zone files have their SOA serial
incremented whenever a real DNS record modification is made.

The goal is to enforce correct DNS behavior by requiring a serial update only when meaningful
changes occur (e.g. IP or record updates), while ignoring non-significant changes such as extra
spaces that will be corrected during code review.

The validation is integrated as a pre-commit hook and only applies to .zone files.

Ref T2149

Test 1:

• Modify a .zone file (e.g. change an IP)
• Do not update the SOA serial
• Commit

→ The commit should fail with an error

Test 2:

• Make a non-significant change (e.g. extra spaces or formatting)
• Do not update the SOA serial
• Commit

→ No error should occur