Support for Custom URI Schemes in OAuth2 Redirect URIs (#37356)

Fix #34349

By the way, remove `(ctx *APIContext) HasAPIError() ` and `(ctx
*APIContext) GetErrMsg()` because they do nothing, the error handling
has been done in API's middeware

The existing OAuth2 tests were not quite right, refactored them together

models/fixtures/oauth2_application.yml

@@ -4,7 +4,7 @@
   name: "Test"
   client_id: "da7da3ba-9a13-4167-856f-3899de0b0138"
   client_secret: "$2a$10$UYRgUSgekzBp6hYe8pAdc.cgB4Gn06QRKsORUnIYTYQADs.YR/uvi" # bcrypt of "4MK8Na6R55smdCY0WuCCumZ6hjRPnGY5saWVRHHjJiA=
-  redirect_uris: '["a", "https://example.com/xyzzy"]'
+  redirect_uris: '["https://example.com"]'
   created_unix: 1546869730
   updated_unix: 1546869730
   confidential_client: true

models/fixtures/oauth2_authorization_code.yml

@@ -1,17 +1,2 @@
-- id: 1
-  grant_id: 1
-  code: "authcode"
-  code_challenge: "CjvyTLSdR47G5zYenDA-eDWW4lRrO8yvjcWwbD_deOg" # Code Verifier: N1Zo9-8Rfwhkt68r1r29ty8YwIraXR8eh_1Qwxg7yQXsonBt
-  code_challenge_method: "S256"
-  redirect_uri: "a"
-  valid_until: 3546869730
-
-- id: 2
-  grant_id: 4
-  code: "authcodepublic"
-  code_challenge: "CjvyTLSdR47G5zYenDA-eDWW4lRrO8yvjcWwbD_deOg" # Code Verifier: N1Zo9-8Rfwhkt68r1r29ty8YwIraXR8eh_1Qwxg7yQXsonBt
-  code_challenge_method: "S256"
-  redirect_uri: "http://127.0.0.1/"
-  valid_until: 3546869730
-
+[]
 # DO NOT add more test data in the fixtures, test case should prepare their own test data separately and clearly