POC: invite users to an Organization

Related to https://gitlab.com/gitlab-com/gitlab-OKRs/-/work_items/7226.

The POC should cover the following flows from the OKR:

• admin can create a new Organization along with a new Organization Owner user
• Organization Owners can invite a new user to an Organization with the following steps:
  1. Organization Owner enters the user email address and invite email is sent
  2. user accepts the email
  3. new user is created
  4. user is onboarded to the Organization and becomes an Organization User

Question to answer:

• Can we implement the organization invite flow that is independent of the login method? In other words, can it support all types of login methods, including passwords, LDAP, SAML, and other OmniAuth providers.