if milvus has multi replica and multi proxy, in case of each proxy
access all replicas, we can add router from proxy to replica, which
means assign replicas to all proxy, each proxy got same number of
replicas, then only access those replicas.

Notice when the goal of evenly assign all replicas to proxies can't be
achieved, fallback to share all replicas between proxies.

Signed-off-by: Wei Liu <[email protected]>

Signed-off-by: Wei Liu <[email protected]>

Signed-off-by: Wei Liu <[email protected]>