sonic: add sonic-vm lab builder support, SonicValidator, and sonic_ebgp lab

[dhalperi]

Add a SONiC (containerlab sonic-vm) vendor profile to lab_builder:
eth1->Ethernet0 port mapping with a stride of 4, BGP health and
validate checks, and packaging of config_db.json and frr.conf under
sonic_configs//. build-sonic-image.sh builds the vrnetlab image
from the public SONiC VS build and caches it in S3; it patches the
wrapper's startup-config restore from "config replace", which stalls on
202605 and leaves bgpd on the default ASN, to "config reload" followed
by a bgp restart.

Replace the SonicValidator stub. Main RIB validation reuses the FRR
validator with a parser for FRR 8+ per-VRF route JSON; interface
validation and runtime data come from SONiC "show interfaces status".

Add sonic_ebgp, a two-node eBGP lab on SONiC 202605. Interface
properties are sickbayed on Batfish's missing SONiC port bandwidth
(#232); BGP RIB validation is not implemented.
sonic_bgp_lab lacks the new validator inputs, so its interface and RIB
tests no longer run.

---

Prompt:

Can we add support for SONiC routers to lab validation?

Follow-ups: the project is not migration-only, so new code is fine; use
a current SONiC image (202605) rather than 202411; send one PR with the
infra, validator fixes, and first lab.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 62.76596% with 35 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.58%. Comparing base (29bf05f) to head (8897ab5).

Files with missing lines	Patch %	Lines
src/lab_validation/validators/SonicValidator.py	36.53%	33 Missing ⚠️
...ab_validation/parsers/sonic/commands/interfaces.py	95.00%	1 Missing ⚠️
...c/lab_validation/validators/CumulusFrrValidator.py	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #233      +/-   ##
==========================================
- Coverage   83.99%   83.58%   -0.42%     
==========================================
  Files          94       96       +2     
  Lines        4618     4703      +85     
==========================================
+ Hits         3879     3931      +52     
- Misses        739      772      +33     

Flag	Coverage Δ
unittests	83.58% <62.76%> (-0.42%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.