Update flow for Cody signup

[fabicastp]

We would like to update the modal that appears that new users see on sourcegraph.com after creating an account.

Today, this modal is served to new users:

We would like to change this to a new modal:

Heading: Would you like to learn more about Cody for enterprise? Subhead: If you're not ready for a conversation, we'll stick to sharing Cody onboarding resources. Buttons:

• Yes, please contact me to set up a call.
• No, thanks.

Neither check box should be required, and users can hit "Get started" to dismiss the modal without selecting either box. Users should not be able to select both boxes.

If a user selects the "Yes" checkbox, more fields will appear for first name, last name, email, phone, and company. These fields should all be required to be filled out in order for the user to click "Get started".

These fields will come from a new HubSpot form that will have to be built into the modal. This is the Form ID and code to embed that HubSpot form:

Form id:

[gitstart-app[bot]]

Here is the GitStart Ticket for this issue: https://clients.gitstart.com/sourcegraph/3436/tickets/SGM-6815

[gitstart-sourcegraph]

Here is the PR