feat(saml): allow setting nameid-format and alternative mapping for transient format (#7979)

# Which Problems Are Solved

ZITADEL currently always uses
`urn:oasis:names:tc:SAML:2.0:nameid-format:persistent` in SAML requests,
relying on the IdP to respect that flag and always return a peristent
nameid in order to be able to map the external user with an existing
user (idp link) in ZITADEL.
In case the IdP however returns a
`urn:oasis:names:tc:SAML:2.0:nameid-format:transient` (transient)
nameid, the attribute will differ between each request and it will not
be possible to match existing users.

# How the Problems Are Solved

This PR adds the following two options on SAML IdP:
- **nameIDFormat**: allows to set the nameid-format used in the SAML
Request
- **transientMappingAttributeName**: allows to set an attribute name,
which will be used instead of the nameid itself in case the returned
nameid-format is transient

# Additional Changes

To reduce impact on current installations, the `idp_templates6_saml`
table is altered with the two added columns by a setup job. New
installations will automatically get the table with the two columns
directly.
All idp unit tests are updated to use `expectEventstore` instead of the
deprecated `eventstoreExpect`.

# Additional Context

Closes #7483
Closes #7743

---------

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

internal/api/idp/idp.go

@@ -229,11 +229,6 @@ func (h *Handler) handleACS(w http.ResponseWriter, r *http.Request) {
 		http.Error(w, err.Error(), http.StatusBadRequest)
 		return
 	}
-	sp, err := samlProvider.GetSP()
-	if err != nil {
-		http.Error(w, err.Error(), http.StatusBadRequest)
-		return
-	}
 
 	intent, err := h.commands.GetActiveIntent(ctx, data.RelayState)
 	if err != nil {
@@ -245,10 +240,10 @@ func (h *Handler) handleACS(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	session := saml2.Session{
-		ServiceProvider: sp,
-		RequestID:       intent.RequestID,
-		Request:         r,
+	session, err := saml2.NewSession(samlProvider, intent.RequestID, r)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusBadRequest)
+		return
 	}
 
 	idpUser, err := session.FetchUser(r.Context())