Add "Sign In" form directly to Element front page

### Your use case

#### What would you like to do?
Add "Sign In" form directly to front page with "Welcome to Element" title, to exclude additional click and wait for new page to load.

#### Why would you like to do it?
When user opens a new Element instance, they want to make the "Sign In" action most of the times, and sometimes "Create account" or "Explore rooms", when it is a new user.

But why with that most popular action we force them to do an additional click to "Sign In" button (with waiting for new form to be loaded) all the times? Let's integrate the "Sign In" form directly in front page (with keeping "Create account" and "Explore rooms" buttons in some visible places)!

And if user have some autofill extension enabled, those fields will be even auto-filled, so user will need only to click "Sign In" button to successfully log in! It will be very convenient!

### Have you considered any alternatives?

_No response_

### Additional context

_No response_