Add ability to set multiple redirect URIs in OAuth application UI (#25072)

OAuth applications can already have multiple redirect URIs if
created/edited over API.

This change allows for setting multiple redirect URIs through the UI as
a comma-separated list (e. g.
`https://example.org/redirect,https://redirect.example.org`)

<details>
<summary>Screenshots</summary>

![Bildschirmfoto vom 2023-06-04
17-14-40](2206dc32-e7e4-4953-9ecb-e098890b3f54)
![Bildschirmfoto vom 2023-06-04
17-14-50](cd97c73c-9310-44ee-a83a-b927a1ef94da)

</details>

Closes #25068

routers/web/user/setting/oauth2_common.go

@@ -10,6 +10,7 @@ import (
 	"code.gitea.io/gitea/models/auth"
 	"code.gitea.io/gitea/modules/base"
 	"code.gitea.io/gitea/modules/context"
+	"code.gitea.io/gitea/modules/util"
 	"code.gitea.io/gitea/modules/web"
 	"code.gitea.io/gitea/services/forms"
 )
@@ -40,7 +41,7 @@ func (oa *OAuth2CommonHandlers) AddApp(ctx *context.Context) {
 	// TODO validate redirect URI
 	app, err := auth.CreateOAuth2Application(ctx, auth.CreateOAuth2ApplicationOptions{
 		Name:               form.Name,
-		RedirectURIs:       []string{form.RedirectURI},
+		RedirectURIs:       util.SplitTrimSpace(form.RedirectURIs, "\n"),
 		UserID:             oa.OwnerID,
 		ConfidentialClient: form.ConfidentialClient,
 	})
@@ -93,7 +94,7 @@ func (oa *OAuth2CommonHandlers) EditSave(ctx *context.Context) {
 	if ctx.Data["App"], err = auth.UpdateOAuth2Application(auth.UpdateOAuth2ApplicationOptions{
 		ID:                 ctx.ParamsInt64("id"),
 		Name:               form.Name,
-		RedirectURIs:       []string{form.RedirectURI},
+		RedirectURIs:       util.SplitTrimSpace(form.RedirectURIs, "\n"),
 		UserID:             oa.OwnerID,
 		ConfidentialClient: form.ConfidentialClient,
 	}); err != nil {