Try to capture email address on self hosted install

[dabeeeenster]

When going through the browser onboarding flow on first deploying self hosted/open source flagsmith, it would be good to offer people to submit their email address so we can follow up with support and possible upgrades.

This could be a form that shows when creating a new organisation, that HTTP POSTs to either a Hubspot URL (ideally) or failing that an endpoint we host (possibly in Vercel? or our core API) and gets the email into Hubspot for further workflow.

Some notes:

• It should be optional.
• We need to figure out decent copy here on why we are asking for it
• We need to store the state of this form against the install so it only ever shows once

[matthewelwell]

As per #3896, we should also optionally capture company information here.

[matthewelwell]

@kyle-ssg first item here is to look at e.g. metabase's onboarding flow.