Refactor codebase, introduce relaymode package, update constants and improve consistency

- Refactor constant definitions and organization
- Clean up package level variables and functions
- Introduce new `relaymode` and `apitype` packages for constant definitions
- Refactor and simplify code in several packages including `openai`, `relay/channel/baidu`, `relay/util`, `relay/controller`, `relay/channeltype`
- Add helper functions in `relay/channeltype` package to convert channel type constants to corresponding API type constants
- Remove deprecated functions such as `ResponseText2Usage` from `relay/channel/openai/helper.go`
- Modify code in `relay/util/validation.go` and related files to use new `validator.ValidateTextRequest` function
- Rename `util` package to `relaymode` and update related imports in several packages

relay/adaptor/azure/helper.go

@@ -0,0 +1,15 @@
+package azure
+
+import (
+	"github.com/gin-gonic/gin"
+	"github.com/songquanpeng/one-api/common/config"
+)
+
+func GetAPIVersion(c *gin.Context) string {
+	query := c.Request.URL.Query()
+	apiVersion := query.Get("api-version")
+	if apiVersion == "" {
+		apiVersion = c.GetString(config.KeyAPIVersion)
+	}
+	return apiVersion
+}