HTTP API: make GET /api/aliveness-test a no-op (backport #13052)

[mergify]

This follows the decision that was made for
'rabbitm-diagnostics node_health_check' which
is a no-op as of 4.0.0 following a few years of
deprecation.

The justification is very similar:

1. There is no such thing as "One True Health Check". A single health check is too coarse-grained to explain what specifically is not right about cluster state
2. Indivual fine-grained health checks have been available for a few years now, see https://www.rabbitmq.com/docs/monitoring#health-checks
3. This particular check tests something that effectively never fails, based on my 14+ years of RabbitMQ contributions and user support of all shapes and forms
4. This check uses a deprecated feature: a non-exclusive non-durable/transient classic queue,
   which it keeps around by design to avoid adding to churn /api/aliveness-test/vhost uses deprecated feature transient_nonexcl_queues with RabbitMQ 4.0.x #13047
5. Earlier this endpoint was removed from the HTTP API reference

If something about this health check is worth
preserving, we can always add a new one
under GET /api/health/checks/*

Closes #13047.

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This is an automatic backport of pull request #13052 done by [Mergify](https://mergify.com).