feat(idp): provide auto only options (#8420)

# Which Problems Are Solved

As of now, **automatic creation** and **automatic linking options** were
only considered if the corresponding **allowed option** (account
creation / linking allowed) was enabled.

With this PR, this is no longer needed and allows administrators to
address cases, where only an **automatic creation** is allowed, but
users themselves should not be allowed to **manually** create new
accounts using an identity provider or edit the information during the
process.
Also, allowing users to only link to the proposed existing account is
now possible with an enabled **automatic linking option**, while
disabling **account linking allowed**.

# How the Problems Are Solved

- Check for **automatic** options without the corresponding **allowed**
option.
- added technical advisory to notify about the possible behavior change

# Additional Changes

- display the error message on the IdP linking step in the login UI (in
case there is one)
- display an error in case no option is possible
- exchanged deprecated `eventstoreExpect` with `expectEventstore` in
touched test files

# Additional Context

closes https://github.com/zitadel/zitadel/issues/7393

---------

Co-authored-by: Stefan Benz <46600784+stebenz@users.noreply.github.com>

internal/api/ui/login/external_provider_handler.go

@@ -533,9 +533,10 @@ func (l *Login) externalUserNotExisting(w http.ResponseWriter, r *http.Request,
 		}
 	}
 
-	// if auto creation or creation itself is disabled, send the user to the notFoundOption
-	if !provider.IsCreationAllowed || !provider.IsAutoCreation {
-		l.renderExternalNotFoundOption(w, r, authReq, orgIAMPolicy, human, idpLink, err)
+	// if auto creation is disabled, send the user to the notFoundOption
+	// where they can either link or create an account (based on the available options)
+	if !provider.IsAutoCreation {
+		l.renderExternalNotFoundOption(w, r, authReq, orgIAMPolicy, human, idpLink, nil)
 		return
 	}
 
@@ -614,6 +615,10 @@ func (l *Login) renderExternalNotFoundOption(w http.ResponseWriter, r *http.Requ
 		l.renderError(w, r, authReq, err)
 		return
 	}
+	if !idpTemplate.IsCreationAllowed && !idpTemplate.IsLinkingAllowed {
+		l.renderError(w, r, authReq, zerrors.ThrowPreconditionFailed(nil, "LOGIN-3kl44", "Errors.User.ExternalIDP.NoOptionAllowed"))
+		return
+	}
 
 	translator := l.getTranslator(r.Context(), authReq)
 	data := externalNotFoundOptionData{