rpk fails to connect to an ipv6 admin-api address

[sundbry]

I am running redpanda in an ipv6 only environment, and the admin-api is listening on a private ipv6 address. I attempted to use rpc to show the cluster health.

Version & Environment

Redpanda version: (use rpk version):

rpk version
Version:     v24.1.7
Git ref:     53e6eab6ab
Build date:  2024-06-06T19:49:38Z
OS/Arch:     linux/amd64
Go version:  go1.22.2

What went wrong?

redpanda@redpanda1:/$ rpk cluster health
unable to initialize admin client: invalid host "[[fddb:1e1b:80b7:c98f:c0df:c5d3:8685:4141]]:9644" does not match "host", nor "host:port", nor "scheme://host:port"

What should have happened instead?

The IPv6 compatible host:port should take the form [fddb:1e1b:80b7:c98f:c0df:c5d3:8685:4141]:9644 and rpk should print the cluster health.

How to reproduce the issue?

redpanda.yaml

redpanda:
    data_directory: /var/lib/redpanda/data
    seed_servers: []
    rpc_server:
        address: "fddb:1e1b:80b7:c98f:c0df:c5d3:8685:4141"
        port: 33145
    kafka_api:
        - address: "fddb:1e1b:80b7:c98f:c0df:c5d3:8685:4141"
          port: 9092
    admin:
        - address: "fddb:1e1b:80b7:c98f:c0df:c5d3:8685:4141"
          port: 9644
    advertised_rpc_api:
        address: "fddb:1e1b:80b7:c98f:c0df:c5d3:8685:4141"
        port: 33145
    advertised_kafka_api:
        - address: "fddb:1e1b:80b7:c98f:c0df:c5d3:8685:4141"
          port: 9092
    developer_mode: false
    auto_create_topics_enabled: true
    fetch_reads_debounce_timeout: 10
    group_initial_rebalance_delay: 0
    group_topic_partitions: 3
    log_segment_size_min: 1
    storage_min_free_bytes: 10485760
    topic_partitions_per_shard: 1000
    write_caching_default: "true"
rpk:
    overprovisioned: false
    coredump_dir: /var/lib/redpanda/coredump
pandaproxy:
    pandaproxy_api:
        - address: "fddb:1e1b:80b7:c98f:c0df:c5d3:8685:4141"
          port: 8082
schema_registry:
    schema_registry_api:
        - address: "fddb:1e1b:80b7:c98f:c0df:c5d3:8685:4141"
          port: 8081

JIRA Link: CORE-7340