fix (MQ): support IPv4-only broker hostnames

[hanx-hep]

Summary

• resolve STOMP broker addresses with AF_UNSPEC so IPv4-only hostnames work
• preserve the existing IPv6 preference and randomized order within each address family
• add unit coverage for IPv4-only, dual-stack, and resolution failure cases

Root cause

The connector queried AF_INET6 before AF_INET. On systems where an IPv4-only
hostname causes the IPv6 lookup to raise socket.gaierror, setup returned early
and never attempted the valid IPv4 addresses.

The same resolution logic is present in rel-v9r0 and rel-v8r0, so this fix
should also be considered for backporting to those maintained release branches.

Validation

79 passed in 0.66s

BEGINRELEASENOTES

*Resources

FIX: Allow STOMP MQ connections to use IPv4-only broker hostnames.

ENDRELEASENOTES

[fstagni]

Thank you for the contribution. Any reason for keeping it in draft?

[hanx-hep]

Thank you for the contribution. Any reason for keeping it in draft?

Hi. No specific reason. I opened it as draft while double-checking the contribution flow. It is ready for review now.

[fstagni]

Apart from the commit message (see failing check, this LGTM).
But, I think you want to backport this to older branches, meaning rel-v9r0 and rel-v8r0. Once done, I will merge them all together.

[hanx-hep]

Thanks. I removed the merge commit from this PR branch and created the requested backport PRs:

• fix (MQ): support IPv4-only broker hostnames #8678 for rel-v9r0
• fix (MQ): support IPv4-only broker hostnames #8679 for rel-v8r0

The MessageQueue tests pass on both backport branches.