Add FRR structured output for BGP Routes

[chriswiggins]

Description

Added a new builtin directive to enable BGP Table structured output from FRR.

This does not do structured output for AS Path or Communities, as both of those outputs from FRR follow very different formats.

There have also been some tweaks to the original parsing that was implemented ~4 years ago (but not actually being used anywhere):

• localpref is now locPrf
• Some of the values now have defaults (I have routes without med, aggregator info, weight or metrics)

Related Issues

N/A

Motivation and Context

I wanted nice BGP Route table output 😆

Tests

Added in a test_bgp_route_frr.py, and updated the sample to exclude some of the values we expect to have missing.

Tested against FRRouting 10.1.1