Sign up UI for Percona Account inside PMM Server

User Story:

As a PMM user (all Grafana roles) I need to be able to sign up for Percona Platform  by providing my separate email and password so that I can sign in to Percona account later

2) After successful  sing up user must be automatically signed in into Percona Account 

Additionally:
1) We need to add the Sign in button on this form to make sure the user can go back and forth between the two screens. It will be disabled before we deliver PMM-6373.

2) The BE API is supposed to return an email in the response object. The presence of the user's email the response means that the user has been successfully signed up and logged in to the Platform.

3) If the user refreshes the browser, we call /v1/Settings/Get and checks for the presence of an object { saas: { email: "user.example.com" }}, which, if present, confirms that the user is both signed up and logged in.

DESIGN (second slide from the url below):

https://www.figma.com/proto/fhRyxGJIQH9VOFTabyPDKe/PMM-Settings-Log-in?scaling=min-zoom&node-id=66%3A399