feat: support cohere rerank

relay/channel/cohere/constant.go

@@ -2,6 +2,7 @@ package cohere
 
 var ModelList = []string{
 	"command-r", "command-r-plus", "command-light", "command-light-nightly", "command", "command-nightly",
+	"rerank-english-v3.0", "rerank-multilingual-v3.0", "rerank-english-v2.0", "rerank-multilingual-v2.0",
 }
 
 var ChannelName = "cohere"