Allow netbox to be a source of truth in discovering devices.

[i3149]

Given a disco config like

discovery:
    cidrs: []
    ignore_list: []
    debug: false
    ports:
        - 161
    default_communities:
        - public
    use_snmp_v1: false
    default_v3: null
    add_devices: true
    add_mibs: false
    threads: 4
    replace_devices: true
    no_dedup_engine_id: true
    kentik: null
    no_use_bulkwalkall: false
    netbox_host: https://yyyy.cloud.netboxapp.com
    netbox_token: ${NETBOX_TOKEN}
    netbox_tag: Foxtrot
    netbox_site: Sydney

ktranslate will now use netbox to find devices to poll vs doing a network scan. Lets you filter by tag and site.

netbox_token can be either written directly into the yaml, passed in via environment variable, or else found via AWS, GCP or Azure vaults.