Add stripe checkout

[pydanny]

Initially we'll use Stripe for financial donations. Notes:

• Link to Stripe checkout
• Must be able to take payments of $5, $50, or variable depending on user submission
• Secrets keys to be controlled by environment variables

For an example of how to execute on this, see this API file.

Dependent on #1 and #4

[pydanny]

Imported the API file from 2784440. Not tested in any way.

[Sahil-101]

hey @pydanny! I would like to work on this issue.