Invite Flow for Self-Hosted portal throws 404

## Bug description

We're self hosting the developer portal as a static website in a storage account. I've updated the notification template to use the URL of the self hosted portal and the invite link is being sent out as follows:

https://sa-name.z19.web.core.windows.net/confirm-v2/identities/basic/invite?userid=id&identity=identity&ticketid=ticketid&ticket=ticket (scrubbed values)

When I click on the link though, it sends me to the 404 page of the self hosted portal. If I change the hostname of the URL to point to the Azure hosted developer portal, i.e. https://api-name.developer.azure-api.net/confirm-v2/identities/basic/invite?rest-of-query, the url works and properly redirects me to the confirm-password page, but this is not working for the self-hosted flow

## Reproduction steps

1. Self-host the developer portal using a static website as outlined here - https://docs.microsoft.com/en-us/azure/api-management/developer-portal-self-host (including updating the notification templates to point to your self-hosted portal)
2. Go to your APIM instance within the azure portal
3. Click on the Users blade
4. Click on the Invite button
5. Fill out the information and send the invitation
6. Open the invitation from the email it was sent to and click on the invite link
7. The link directs you to the 404 page specified in your self hosted developer portal

## Expected behavior

Steps 1-6 as outlined above, but step 7 should redirect you to the confirm-password page where the user is then able to create a password for their account.

## Is your portal managed or self-hosted?
Self-hosted

## Release tag or commit SHA (if using self-hosted version)
commit/c523c10a7ab07eb10842e8d909d62fd141bfd9bf

## API Management service name
Reach out if this is needed

## Environment

- Operating system: Windows 10 Enterprise 64-bit
- Browser: Firefox
- Version: 91.0

## Additional context

The flow does work on the managed portal but fails for the self hosted portal. I also believe that clicking on the invitation link does actually activate the user's account, but doesn't allow them to confirm their password. Updating the verbiage at https://docs.microsoft.com/en-us/azure/api-management/developer-portal-self-host#invite-user would help remove some of the confusion I had here

The issue names no source file or test. Start by reproducing the invitation-link flow on the self-hosted portal at commit c523c10a7ab07eb10842e8d909d62fd141bfd9bf, then compare it with the working managed-portal URL and the self-hosting configuration. Done means the self-hosted invite link reaches the confirm-password page instead of the portal's 404 page.

Written by the indexing model from the issue text.