Fix type issues with using sdwan_security_policy in unified mode

[seconroy]

Description

Fix type issues with unified security policy, specifically:

• Convert imcp_unreachable_allow, session_reclassify_allow, and unified_logging to type string with enum values of on or off
• Converts max_incomplete_icmp_limit, max_incomplete_tcp_limit, and max_incomplete_upd_limit to type string
• Converts source_zone and destination_zone fields to entries list containing source_zone/destination_zone objects to support multiple entries

Types of Changes

• New feature (non-breaking change which adds functionality)
• Bug fix (non-breaking change which fixes an issue)
• Breaking change (fix or feature that would cause existing functionality to change)
• Build/CI change
• Code quality improvement/refactoring/documentation (no functional changes)

Checklist

• My code follows the code style of this project
• I have added tests to cover my changes
• All new and existing tests pass locally