refactor: "install" page (#39400)

1. remove useless options
2. set AppDataPath instead of repo root path
3. make "disable self-registration" default enabled
4. avoid writing corrupted ini file
5. avoid auto-sign-in the existing admin user

modules/auth/webauthn/webauthn.go

@@ -29,7 +29,7 @@ func Init() {
 	WebAuthn = &webauthn.WebAuthn{
 		Config: &webauthn.Config{
 			RPDisplayName:         setting.AppName,
-			RPID:                  setting.Domain,
+			RPID:                  setting.AppDomain,
 			RPOrigins:             []string{appURL},
 			AttestationPreference: protocol.PreferNoAttestation, // Gitea never verifies attestation
 		},

modules/auth/webauthn/webauthn_test.go

@@ -12,14 +12,14 @@ import (
 )
 
 func TestInit(t *testing.T) {
-	setting.Domain = "domain"
+	setting.AppDomain = "domain"
 	setting.AppName = "AppName"
 	setting.AppURL = "https://domain/"
 	rpOrigin := []string{"https://domain"}
 
 	Init()
 
-	assert.Equal(t, setting.Domain, WebAuthn.Config.RPID)
+	assert.Equal(t, setting.AppDomain, WebAuthn.Config.RPID)
 	assert.Equal(t, setting.AppName, WebAuthn.Config.RPDisplayName)
 	assert.Equal(t, rpOrigin, WebAuthn.Config.RPOrigins)
 }