Remove user migration workflow

[rustyjux]

Background

User migration workflows were created to support Keycloak migration from Silver to Gold (see https://dpdd.atlassian.net/issues/APS-1335, #580, #605), namely to add logic to login to migrate a user's Authz permissions from their old user (username@provider) to the new user (user_uuid@provider) and to disable the old user.

This was implemented in v1.2.5 of Portal in Oct 2022 and so all users should be migrated at this point and this functionality (and the associated tests) are likely no longer required.

While working on a Portal Node upgrade, the tests for user migration were leading to Portal crashes and providing the impetus to open this issue.

User migration functionality is in src/services/workflow/migrate-user.ts and referenced by src/auth/auth-oauth2-proxy.js. Tested in e2e/cypress/tests/05-migrate-user/01-migrate-user-access.cy.ts.

A/C

• confirm user migration workflow is no longer required
  • review old users still in Keycloak (prod)
• user migration functionality is removed
• related tests are removed