feat: Add Baidu Qianfan V2 channel support #725

- Update channel constants to include Baidu V2 channel
- Create new Baidu V2 adaptor for relay
- Add Baidu V2 models and channel configuration
- Update relay adaptor to support Baidu V2 channel
- Modify web channel constants to include Baidu V2 option

relay/channel/baidu_v2/constants.go

@@ -0,0 +1,29 @@
+package baidu_v2
+
+var ModelList = []string{
+	"ernie-4.0-8k-latest",
+	"ernie-4.0-8k-preview",
+	"ernie-4.0-8k",
+	"ernie-4.0-turbo-8k-latest",
+	"ernie-4.0-turbo-8k-preview",
+	"ernie-4.0-turbo-8k",
+	"ernie-4.0-turbo-128k",
+	"ernie-3.5-8k-preview",
+	"ernie-3.5-8k",
+	"ernie-3.5-128k",
+	"ernie-speed-8k",
+	"ernie-speed-128k",
+	"ernie-speed-pro-128k",
+	"ernie-lite-8k",
+	"ernie-lite-pro-128k",
+	"ernie-tiny-8k",
+	"ernie-char-8k",
+	"ernie-char-fiction-8k",
+	"ernie-novel-8k",
+	"deepseek-v3",
+	"deepseek-r1",
+	"deepseek-r1-distill-qwen-32b",
+	"deepseek-r1-distill-qwen-14b",
+}
+
+var ChannelName = "volcengine"