feat: 添加Mistral渠道 (close #546)

relay/channel/mistral/constants.go

@@ -0,0 +1,12 @@
+package mistral
+
+var ModelList = []string{
+	"open-mistral-7b",
+	"open-mixtral-8x7b",
+	"mistral-small-latest",
+	"mistral-medium-latest",
+	"mistral-large-latest",
+	"mistral-embed",
+}
+
+var ChannelName = "mistral"