Pending subscription requests can slow down index page
When a user is logged-in, we check if there are any pending subscription requests for the user and this can take a significant amount of time on lists where there are a lot of pending requests. For example: https://mail.python.org/mailman3/lists/python-dev.python.org/ takes about 7 seconds to open, which is really not nice.
We need a better way to check for pending subscription for a email address, perhaps an extra endpoint to check if there is a subscription request pending for an email instead of getting all and iterating over it.