Set default active tab for Donation Block

### What

The donation block has the is-active class set by default on the “one-time” heading which then triggers the content inside the tab to change. The suggestion is that we provide a way for the user to select or change the default tab (i.e. monthly, annually).

### Why

Currently, the only way to do this would be for the user to add custom JS through a plugin. This would erase that need.

### How

Locate the Donation Block implementation and the logic that assigns the default is-active class to the one-time tab. Review the screenshots and trace how tab content changes. Done means users can select monthly or annually as the default tab without adding custom JavaScript.

Written by the indexing model from the issue text.