fix: loosen agent version checking

- warn instead of error when version mismatch
- check for major version only
- better version parsing

internal/api/v1/version.go

@@ -1,12 +0,0 @@
-package v1
-
-import (
-	"net/http"
-
-	"github.com/yusing/go-proxy/internal/net/gphttp"
-	"github.com/yusing/go-proxy/pkg"
-)
-
-func GetVersion(w http.ResponseWriter, r *http.Request) {
-	gphttp.WriteBody(w, []byte(pkg.GetVersion()))
-}