ThinkLinks: make the SSO sign-in timeout configurable

What is wanted

A configurable timeout for ThinkLinks sign-in. At present the timeout is fixed, so a slow round trip to ThinkAuth can fail the sign-in rather than waiting a moment longer.

Why it matters here

ThinkLinks talks to ThinkAuth over the network, and when ThinkAuth is briefly busy the request can exceed the built-in limit. Being able to raise it via configuration would absorb that instead of turning a slow login into a failed one.

Why it is Upstream

There is no setting to change on our side — the timeout is hardcoded in Linkwarden, the application behind ThinkLinks. Requested upstream as linkwarden/linkwarden#788. This post tracks it.