fix(oidc): enable webkey feature by default (#10683)

# Which Problems Are Solved

When the webkey feature flag was not enabled before an upgrade to v4,
all JWT tokens became invalid.
This created a couple of issues:

- All users with JWT access tokens are logged-out
- Clients that are unable to refresh keys based on key ID break
- id_token_hint could no longer be validated.

# How the Problems Are Solved

Force-enable the webkey feature on the v3 version, so that the upgrade
path is cleaner. Sessions now have time to role-over to the new keys
before initiating the upgrade to v4.

# Additional Changes

- none

# Additional Context

- Related https://github.com/zitadel/zitadel/issues/10673

---------

Co-authored-by: Livio Spring <livio.a@gmail.com>

internal/api/oidc/integration_test/keys_test.go

@@ -25,6 +25,10 @@ import (
 
 func TestServer_Keys(t *testing.T) {
 	instance := integration.NewInstance(CTX)
+	// As we want to test the legacy keys as well, we need to ensure the webkey feature is off
+	// at the beginning since the instance creation enables it by default.
+	ensureWebKeyFeature(t, instance, false)
+
 	ctxLogin := instance.WithAuthorization(CTX, integration.UserTypeLogin)
 
 	clientID, _ := createClient(t, instance)