Enable setting session cookie attributes from ui.run()

[samuller]

Motivation

When using app.storage.user it creates a session cookie with permissions that disallow cross-origin usage. While this is a good secure default, there's currently no way to override it when needed, e.g. if you want your NiceGUI site to be embeddable as an iframe from another domain. See discussion #4252.

Implementation

A new argument is added to ui.run() which allows passing keyword arguments that will be forwarded to the SessionMiddleware that is used to create the session cookie.

Progress

• I chose a meaningful title that completes the sentence: "If applied, this PR will..."
• The implementation is complete.
• Pytests have been added (or are not necessary).
• Documentation has been added (or is not necessary).