Manage Credited members in UI

[Ranthalion]

Create admin/leadership functionality to manage member credits.

Member credits are manually assigned by leadership.
This is to handle the edge case of someone paying for another persons membership (because that shows up as one email)
another example is that we received funding to grant memberships to people who have experienced hardships related to the pandemic which has prevented them from becoming a member.
Currently the credits do not expire automatically. Leadership will have to revoke manually. Which at the moment involves a DB query to change their Membership Level

[dfirebaugh]

I think this can just be added to the "action menu" that shows up when you click the three dots next to a member.

we could show "Make Credited" and if they are already credited we can show a "Remove Credit"