Add support for partitioned session cookies

[bookernath]

Related issue with historical context: pallets/werkzeug#2797

Partitioned cookies are now supported in Werkzeug: pallets/werkzeug#2855

It would be nice to have first-class support for the flask session cookie using the Partitioned flag to provide support for Chrome's CHIPS and allow sessions to continue to work within iframes.

Example usage might be:

app.config['SESSION_COOKIE_SAMESITE'] = "None"
app.config['SESSION_COOKIE_SECURE'] = True
app.config['SESSION_COOKIE_PARTITIONED'] = True # add this?