fix: added login_hint to the idp intent (#11552)

# Which Problems Are Solved

In login V2, when the user started the login flow of an external IDP,
there was no login_hint passed to the external provider. This required
the user to enter their username again. Whilst they already entered it
in Zitadel. By adding the `login_hint` parameter, the username should
already be filled in on the external idp.

# How the Problems Are Solved

Pass the `login_hint` parameter to the external idp.

# Additional Changes

Also added the `login_hint` to the event-store for audit trailing.

# Additional Context


- Closes #11392

---------

Co-authored-by: Copilot <[email protected]>

internal/command/idp_intent_model.go

@@ -21,6 +21,7 @@ type IDPIntentWriteModel struct {
 	IDPUserID    string
 	IDPUserName  string
 	UserID       string
+	LoginHint    string
 
 	IDPAccessToken *crypto.CryptoValue
 	IDPIDToken     string
@@ -97,6 +98,7 @@ func (wm *IDPIntentWriteModel) reduceStartedEvent(e *idpintent.StartedEvent) {
 	wm.SuccessURL = e.SuccessURL
 	wm.FailureURL = e.FailureURL
 	wm.IDPID = e.IDPID
+	wm.LoginHint = e.LoginHint
 	wm.IDPArguments = e.IDPArguments
 	wm.State = domain.IDPIntentStateStarted
 }