fix(oauth2): persist linkAccountData during auto-link 2FA flow (#38274) (#38295)

Backport #38274 by @afahey03

Fixes HTTP 500 when OIDC auto account linking (`ACCOUNT_LINKING=auto`)
requires local 2FA. `oauth2LinkAccount` set `linkAccount` in the session
before redirecting to 2FA but did not persist `linkAccountData`, so
`TwoFactorPost` failed with `not in LinkAccount session`. The manual
linking flow already stored both, this aligns auto-link with that
behavior.

Created the test, `TestOAuth2AutoLinkWithTwoFactor`, which verifies that
automatic account linking completes after the user passes local 2FA when
an OIDC identity matches an existing account.

DISCLAIMER: I used AI to create the test

Closes #38171

Co-authored-by: Aidan Fahey <afahey2003@yahoo.com>
Co-authored-by: bircni <bircni@icloud.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

routers/common/middleware.go

@@ -147,6 +147,9 @@ func MustInitSessioner() func(next http.Handler) http.Handler {
 		Secure:         setting.SessionConfig.Secure,
 		SameSite:       setting.SessionConfig.SameSite,
 		Domain:         setting.SessionConfig.Domain,
+
+		// in the future, if websocket is used, the websocket handler should manage its own session sync (release)
+		IgnoreReleaseForWebSocket: true,
 	})
 	if err != nil {
 		log.Fatal("common.Sessioner failed: %v", err)