This PR disables the "create feature flag" button when you've reached
the limits.
This one is a little more complex than the other UI limits, because we
also have to take into account the project feature limit. I've tried to
touch as little as possible, but I _have_ extracted the calculation of
both limits into a single hook.
This PR activates the limit for API token creation in both the global
API token window and in the project-level API token tab.
Because the same button is used in two places, I encapsulated the
fetching of flags and resource limits within the button. I can be
convinced to pass the current API token count and the limit as
arguments, but I think this is the right solution for this case.
This PR updates the Unleash UI to use the new environment limit.
As it turns out, we already had an environment limit in the UI, but it
was hardcoded (luckily, its value is the same as the new default value
🥳).
In addition to the existing places this limit was used, it also disables
the "new environment" button if you've reached the limit. Because this
limit already exists, I don't think we need a flag for it. The only
change is that you can't click a button (that should be a link!) that
takes you to a page you can't do anything on.
