mgr/dashboard: fix bind address regression from CherryPy isolation

mgr/dashboard: fix bind address regression from CherryPy isolation

The CherryPy isolation refactor (PR #67227) accidentally changed the
dashboard bind address from wildcard (*:8443) to mon_ip:8443. The
get_mgr_ip() replacement was originally only for URI generation, but
the refactor passed the mutated address to CherryPyMgr.mount() as the
actual socket bind address.

This breaks the management gateway when its VIP is not on the same
interface as mon_ip, as the dashboard becomes unreachable on other
interfaces.

Preserve the original wildcard address for binding and only use
get_mgr_ip() for the advertised URI. Add regression test to prevent
future confusion between bind_addr and server_addr.

Fixes: https://tracker.ceph.com/issues/77491
Signed-off-by: Afreen Misbah <afreen@ibm.com>