Fix BGP Session display under Device view

[Kani999]

Summary

This merge request improves the BGP session display functionality on device detail pages by addressing several usability and performance issues.

Changes Made

🔧 Performance Improvements:

• Originally the large table would be displayed as a whole, now it can be paged
• Replaced manual table rendering with htmx_table for better performance and built-in pagination

🎨 UI/UX Improvements:

• Originally columns would overflow the table, now it takes table configuration from the list view
• Consistent table styling and column configuration across all BGP session views

⚙️ New Configuration Options:

• Originally there was no option to display BGP sessions under a Device View Tab, now it is configurable
• Added new tab display mode to device_ext_page configuration option
• Users can now choose between: left, right, full_width, or tab display modes

Technical Details

• New Tab View: Implemented DeviceBGPSessionTabView using ObjectChildrenView with conditional registration
• Template Optimization: Simplified template extension by removing manual table creation and extra context dependencies
• Configuration Enhancement: Enhanced documentation with detailed explanations of all display modes

Configuration Example

PLUGINS_CONFIG = {
    'netbox_bgp': {
        'device_ext_page': 'tab',  # New option: displays BGP sessions in a dedicated tab
    }
}

Files Modified

• template_content.py - Added tab view and improved template handling
• device_extend.html - Replaced manual table with htmx_table
• README.md - Updated documentation with detailed display mode explanations

Backward Compatibility

✅ All existing display modes (left, right, full_width) continue to work as before
✅ Default behavior remains unchanged (defaults to right)