[White label] Custom domain

[garyhtou]

Don't work on this just yet.

We want to allow organizations to white label this donation page. See the parent issue for more details. Here's how the use flow should work:

1. Enable white labeling in org settings
2. Fill in a "domain" textbox.
3. Use the HCB provided instructions to configure your DNS (similar to Google Workspace). For example:

   Add a CNAME record `donate.example.com` with the value `cname.hcb.hackclub.com`
   

4. On the HCB dashboard, click the very button (or wait for HCB to automatically verify it)
5. Enjoy your new donation page!

Open questions

In the future, do we want to allow this custom domain for transparent mode? Likely yes. If so, it should be forward compatible with rendering more than just the donation page. Thus, the subdomain that people choose likely should be finance.example.com, and the donation page is located at finance.example.com/donate.

[sampoder]

https://github.com/sampoder/bank-custom-domains lol