Only redirect the user to a configured logout page if the logout was user-initiated

### Steps to reproduce

1. Configure a `logout_redirect_url` that points to e.g. the KeyCloak logout url as proposed in #15829.
2. Sign out the session from another device (or via the back-channel-logout or admin api).

### Outcome

#### What did you expect?

The session is stopped and the user sees the login page to login again. The `logout_redirect_url` should only come into effect if the user explicitly logouts of the session from the Element UI itself.

#### What happened instead?

The session is stopped and the user is forwarded to the configured logout URL. It is confusing when a logout happened in the background and the user is unexpectedly forwarded to the logout endpoint when they open Element in the browser.

### Operating system

_No response_

### Browser information

_No response_

### URL for webapp

Private server

### Application version

1.11.31

### Homeserver

Synapse 1.78.0

### Will you send logs?

No