feat(sso): add email domain precheck sso flow

[MarcWadai]

fixes #1094

Changes

• New welcome page
  

• new email check page
  

• New feature flag to activate the view of this flow or not :

tchap_sso_flow: {
  isActive: true
}

• New register page
  

Checklist

• Tests written for new code (and old code if feasible).
• New or updated public/exported symbols have accurate TSDoc documentation.
• Linter and other CI checks pass.
• Sign-off given on the changes (see CONTRIBUTING.md).

[MarcWadai]

The tests on this file are not actually working. There is one mock that have difficulties to be taken into account (registerrequest) ... The correct behavior is that this method will be called and should return 401 Matrix error (if not UIA action), and then show the different component of the registration. However, the mock written for it is bypassed and I couln't figure it out yet.
I am still leaving it like this, because the other part should be correct, and if one day i have the illumination to solve it, it will be here :D