Add a sticky Built with Reflex badge

[Lendemor]

To remove the badge, set SHOW_BUILT_WITH_REFLEX=0 in the environment or in rxconfig.py:

import reflex as rx

config = Config(
    "my_app",
    show_built_with_reflex=False,
)

This setting will be respected on run and export for logged in accounts on team and enterprise tier

This setting will be respected on deploy for logged in accounts on pro, team, and enterprise tier.

When the setting is True and the user is not on a high enough tier, error looks like

Warning: Config option `show_built_with_reflex` is restricted. Your current 
subscription tier is `pro`. Please upgrade to ['team', 'enterprise'] to access 
this option.

If the user is not logged in at all, the error looks like:

Warning: Config option `show_built_with_reflex` is restricted. You are currently
logged out. Run `reflex login` to access this option.

Neither of these errors are fatal, the app will just revert to the default show_built_with_reflex=True

[Lendemor]

How about showing it when --env prod is used ?