Registry client: use a map

[ebullient]

registries:
  registry.other.thing:
  registry.quarkus.io:
    update-policy: "always"
    maven:
      repository:
        url: http://quarkus-registry.squash-club.co.za/maven
  registry.test.local:
    update-policy: "always"
    maven:
      repository:
        url: http://quarkus-registry.squash-club.co.za/maven

Move to a map so we can use keys (more than an array)

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