pack: separate registry list and pack list commands

[pkazmierczak]

Description

This PR changes nomad-pack registry list command to display a list of registries, i.e.:

$ nomad-pack registry list
  REGISTRY NAME |  REF   | LOCAL REF |                    REGISTRY URL
----------------+--------+-----------+-----------------------------------------------------
  community     | latest | bd48167   | github.com/hashicorp/nomad-pack-community-registry

and adds a new nomad-pack list command that lists only packs:

$ nomad-pack list
          PACK NAME          | METADATA VERSION |   REGISTRY NAME
-----------------------------+------------------+--------------------
  alertmanager               | 0.0.1            | community@bd48167
  aws_efs_csi                | 0.0.1            | community@bd48167
  boundary                   | 0.0.1            | community@bd48167
  chaotic_ngine              | 0.0.1            | community@bd48167
  csi_openstack_cinder       | 0.0.1            | community@bd48167
  drone                      | 0.0.1            | community@bd48167
  faasd                      | 0.0.1            | community@bd48167
  fabio                      | 0.0.1            | community@bd48167
  grafana                    | 0.1.0            | community@bd48167
  haproxy                    | 0.0.1            | community@bd48167
  hashicups                  | 0.0.1            | community@bd48167
  hello_world                | 0.0.1            | community@bd48167
  influxdb                   | 0.0.1            | community@bd48167
  jaeger                     | 0.0.1            | community@bd48167
  jenkins                    | 0.0.1            | community@bd48167
  kibana                     | 0.0.1            | community@bd48167
  loki                       | 0.0.1            | community@bd48167
  nextcloud                  | 0.0.1            | community@bd48167
  nginx                      | 0.0.1            | community@bd48167
  nomad_autoscaler           | 0.0.1            | community@bd48167
  nomad_ingress_nginx        | 0.0.1            | community@bd48167
  opentelemetry_collector    | 0.0.1            | community@bd48167
  outline                    | 0.0.1            | community@bd48167
  prometheus                 | 0.0.1            | community@bd48167
  prometheus_consul_exporter | 0.0.1            | community@bd48167
  prometheus_node_exporter   | 0.0.1            | community@bd48167
  prometheus_snmp_exporter   | 0.0.1            | community@bd48167
  promtail                   | 0.0.1            | community@bd48167
  rabbitmq                   | 0.0.1            | community@bd48167
  redis                      | 0.0.1            | community@bd48167
  simple_service             | 0.0.1            | community@bd48167
  sonarqube                  | 0.0.1            | community@bd48167
  tempo                      | 0.0.1            | community@bd48167
  tfc_agent                  | 0.1.0            | community@bd48167
  traefik                    | 0.1.0            | community@bd48167
  vector                     | 0.0.1            | community@bd48167
  wordpress                  | 0.0.1            | community@bd48167

Resolves #354.

Reminders

• Add CHANGELOG.md entry

[shoenig]

LGTM!