feat: federated logout for SAML IdPs (#9931)

# Which Problems Are Solved

Currently if a user signs in using an IdP, once they sign out of
Zitadel, the corresponding IdP session is not terminated. This can be
the desired behavior. In some cases, e.g. when using a shared computer
it results in a potential security risk, since a follower user might be
able to sign in as the previous using the still open IdP session.

# How the Problems Are Solved

- Admins can enabled a federated logout option on SAML IdPs through the
Admin and Management APIs.
- During the termination of a login V1 session using OIDC end_session
endpoint, Zitadel will check if an IdP was used to authenticate that
session.
- In case there was a SAML IdP used with Federated Logout enabled, it
will intercept the logout process, store the information into the shared
cache and redirect to the federated logout endpoint in the V1 login.
- The V1 login federated logout endpoint checks every request on an
existing cache entry. On success it will create a SAML logout request
for the used IdP and either redirect or POST to the configured SLO
endpoint. The cache entry is updated with a `redirected` state.
- A SLO endpoint is added to the `/idp` handlers, which will handle the
SAML logout responses. At the moment it will check again for an existing
federated logout entry (with state `redirected`) in the cache. On
success, the user is redirected to the initially provided
`post_logout_redirect_uri` from the end_session request.

# Additional Changes

None

# Additional Context

- This PR merges the https://github.com/zitadel/zitadel/pull/9841 and
https://github.com/zitadel/zitadel/pull/9854 to main, additionally
updating the docs on Entra ID SAML.
- closes #9228 
- backport to 3.x

---------

Co-authored-by: Silvan <[email protected]>
Co-authored-by: Zach Hirschtritt <[email protected]>

console/src/assets/i18n/ko.json

@@ -2348,6 +2348,8 @@
     "REMOVE_WARN_DESCRIPTION": "ID 제공자를 제거하려고 합니다. 사용자가 선택할 수 있는 ID 제공자가 제거되며, 이미 등록된 사용자는 다시 로그인할 수 없습니다. 계속하시겠습니까?",
     "DELETE_SELECTION_TITLE": "ID 제공자 삭제",
     "DELETE_SELECTION_DESCRIPTION": "ID 제공자를 삭제하려고 합니다. 이 변경 사항은 되돌릴 수 없습니다. 정말로 삭제하시겠습니까?",
+    "FEDERATEDLOGOUTENABLED": "연합 로그아웃 활성화됨",
+    "FEDERATEDLOGOUTENABLED_DESC": "활성화되면 사용자가 ZITADEL에서 세션을 종료할 경우 IdP에서도 로그아웃됩니다.",
     "EMPTY": "사용 가능한 ID 제공자가 없습니다.",
     "OIDC": {
       "GENERAL": "일반 정보",