Feat(eos_cli_config_gen): Add enabled flag to router traffic-engineering

[gmuloc]

Change Summary

This is to be able to render alone

router traffic-engineering

Today it is required to do:

router_traffic_engineering: {}

Which we want to avoid in AVD (having to define an empty dict to generate some conf

The flags is for now optional (it only renders a line in the documentation. It WILL become mandatory in AVD 5.0.0

Component(s) name

arista.avd.eos_cli_config_gen

Proposed changes

Adding enabled flag to router_traffic_engineering

How to test

molecule test allow to verify in doc

Checklist

User Checklist

• open issue for AVD 5.0.0: Refactor(eos_cli_config_gen)!: Make enabled flag required for router_traffic_engineering #3281

Repository Checklist

• My code has been rebased from devel before I start
• I have read the CONTRIBUTING document.
• My change requires a change to the documentation and documentation have been updated accordingly.
• I have updated molecule CI testing accordingly. (check the box if not applicable)

[carlbuchmann]

LGTM tested locally