feat: support configurable captcha(reCaptcha & hCaptcha) (#765)

* feat: support configurable captcha(layered architecture)

* refactor & add captcha logo

* rename captcha

* Update authz.go

* Update hcaptcha.go

* Update default.go

* Update recaptcha.go

Co-authored-by: Gucheng <85475922+nomeguy@users.noreply.github.com>

captcha/provider.go

@@ -0,0 +1,30 @@
+// Copyright 2022 The Casdoor Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package captcha
+
+type CaptchaProvider interface {
+	VerifyCaptcha(token, clientSecret string) (bool, error)
+}
+
+func GetCaptchaProvider(captchaType string) CaptchaProvider {
+	if captchaType == "Default" {
+		return NewDefaultCaptchaProvider()
+	} else if captchaType == "reCAPTCHA" {
+		return NewReCaptchaProvider()
+	} else if captchaType == "hCaptcha" {
+		return NewHCaptchaProvider()
+	}
+	return nil
+}