Implement our own Lando sponsorship mechanism

[pirog]

Based on how easily we get stripe subscriptions rolling for holodroid #149 we might want to consider implementing our own subscription mechanism for lando sponsorships. This would probably:

• Allow us greater control on UI/UX choices
• Provide a more reliable automation flow eg subscribing them to mailchimp etc
• Reduce the steps required to give money
• Allow more complex flows like "thanks for buying a holodroid subscription, do you also want to donate $1 to lando?"
• Potentially net us more money in the long run on fees

Once we have this rolling we could also promote it over other sponsor mechanisms with things like

1. Discounts on holodroid membership
2. Maybe a larger store spend
3. Other ideas TBD

As part of this we might want to consider sunsetting hubspot in favor of using stripe+mailchimp for all of our stuff.