fix: do not inject plugin.RunOn when Kong >= 2.0.0

Kong 2.0.0 removed the `run_on` property on the `plugins` entity.
Controller's code always injects it avoid false positives during diffs.

The change nils the property for Kong 2.0 and above only to avoid any
effect on Kong Enterprise, which follows a different versioning scheme.

From #522
Fix #521

internal/ingress/controller/kong.go

@@ -332,6 +332,7 @@ var (
 	kong110version = semver.MustParse("1.1.0")
 	kong120version = semver.MustParse("1.2.0")
 	kong130version = semver.MustParse("1.3.0")
+	kong200version = semver.MustParse("2.0.0")
 
 	kongEnterprise036version = semver.MustParse("0.36.0")
 )
@@ -387,5 +388,8 @@ func (n *KongController) fillPlugin(plugin *file.FPlugin) error {
 			plugin.Protocols = kong.StringSlice("http", "https")
 		}
 	}
+	if n.cfg.Kong.Version.GTE(kong200version) {
+		plugin.RunOn = nil
+	}
 	return nil
 }