Allow users to customize the name on their billing information

### Expected behavior
- Some people have a different name on their card than their name in Notebook.ai. These users should be able to specify their billing name when subscribing.

### Actual behavior
- The user's `name` field is populated into the billing information.

No files, tests, or entry points are named. Start by locating the subscription billing flow that populates billing information from the user's name, then verify that a separately supplied billing name is used when subscribing while the existing name remains unchanged.

Written by the indexing model from the issue text.