The cluster bus doesn't distinguish between migrations and other actions.
This feature detects a migration by checking if exactly one slot has a new
owner.

Only one moved slot per cluster bus message or command is notified. This
is to avoid flooding the clients. In other cases, such as failovers,
clients will need to handle MOVED redirects and update the slot mapping
accordingly.

A special pubsub channel `__cluster__:moved` is used (naming inspired by
client-side caching). Since the payload of pubsub messages are strings,
it is encoded as a string on the form "MOVED slot endpoint:port", just
like a MOVED redirects.

Some special logic added to avoid creating the pubsub message if there
are no subscribers, and to adjust the port (TLS or non-TLS) to the
receiver's connection.

Signed-off-by: Viktor Söderqvist <viktor.soderqvist@est.tech>

Signed-off-by: Viktor Söderqvist <viktor.soderqvist@est.tech>