Backport of discovery: correctly handle IPv6 addresses from go-discover into release/1.9.x

[hc-github-team-nomad-core]

Backport

This PR is auto-generated from #24649 to be assessed for backporting due to the inclusion of the label backport/1.9.x.

The below text is copied from the body of the original PR.

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Nomad sets a default port when resolving server addresses that don't have one. When we get a "bare" IPv6 address without a port, we end up with an unexpected error "too many colons in address" when we try to split the address and host, because the standard library function expects IPv6 addresses to be wrapped in brackets as recommended by RFC5952. User-configured addresses avoid this problem by accepting IP address and port as separate configuration values, but go-discover emits "bare" IPv6 addresses without a port in IPv6 environments.

Fix this by adding brackets to IPv6 addresses when we get the "too many colons" error from the stdlib. This will still give erroneous results if the address includes the port but is missing brackets, but there's no way to unambiguously parse that address.

Ref: https://www.rfc-editor.org/rfc/rfc5952
Fixes: #24608
Ref: https://hashicorp.atlassian.net/browse/NET-11857

Contributor Checklist

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Overview of commits

• 30e57c3