Added Okta config test with cert chain. (#35159)

<!-- Add the related story/sub-task/bug number, like Resolves #123, or
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**Related issue:** Resolves #34533

Test change only. No functional changes.

# Checklist for submitter

## Testing

- [x] Added/updated automated tests

server/service/integration_enterprise_test.go

@@ -21924,4 +21924,51 @@ FqU+KJOed6qlzj7qy+u5l6CQeajLGdjUxFlFyw==
 		"",
 		0,
 	)
+
+	// Test 9: Set configuration with multiple certificate blocks
+	// This tests that the validation logic properly handles multiple PEM-encoded certificates
+	// Use a second different certificate to simulate a real-world scenario (e.g., certificate chain)
+	secondValidCert := `-----BEGIN CERTIFICATE-----
+MIIGHzCCBAegAwIBAgIBATANBgkqhkiG9w0BAQsFADBSMQswCQYDVQQGEwJVUzEL
+MAkGA1UECBMCTlkxETAPBgNVBAcTCE5ldyBZb3JrMRAwDgYDVQQKEwdFeGFtcGxl
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+-----END CERTIFICATE-----`
+	validCertMultiple := validCert + "\n" + secondValidCert
+	s.DoRaw("PATCH", "/api/latest/fleet/config", oktaPayload(&idp, &acs, &aud, &validCertMultiple), http.StatusOK)
+
+	// Verify the configuration is saved with multiple certificates
+	acResp = appConfigResponse{}
+	s.DoJSON("GET", "/api/latest/fleet/config", nil, http.StatusOK, &acResp)
+	require.True(t, acResp.ConditionalAccess.OktaCertificate.Valid)
+	assert.Equal(t, validCertMultiple, acResp.ConditionalAccess.OktaCertificate.Value)
 }