Add LoginWithEmail to facilitate login with email

[fzaninotto]

Problem

To create a custom login form (e.g., to use email/password instead of userrname/password), developers have to copy an enorm amount of code from react-admin.

Solution

Provide a built-in LoginWithEmail component:

import { Admin, LoginWithEmail } from 'react-admin';
import authProvider from './authProvider';

const App = () => (
    <Admin loginPage={LoginWithEmail} authProvider={authProvider}>
        ...
    </Admin>
);

Improve composition of Login components,to allow to easily add custom content.

import { Box, Link } from '@mui/material';
import { Link as RouterLink } from 'react-router-dom';
import { Login, LoginForm } from 'react-admin';

const MyLogin = () => (
    <Login>
        <LoginForm />
        <Box textAlign="center" mb={1}>
            <Link component={RouterLink} to="/forgot-password">
                Forgot password?
            </Link>
        </Box>
    </Login>
);

I also updated the default login form to use a <PasswordInput> instead of a <TextInput type="password"> so that we benefit from the "show/hide password" button.

How To Test

• The custom login forms of the eCommerce and CRM demos still work, even though 90% of their code was removed.
• The Login story was expanded to cover more cases
• Addes a LoginWithEmail story

Additional Checks

• The PR targets master for a bugfix, or next for a feature
• [ ] The PR includes unit tests (current tests are enough)
• The PR includes one or several stories (if not possible, describe why)
• The documentation is up to date

[fzaninotto]

Notice: I changed TextInput for PasswordInput here.

[fzaninotto]

Couldn't use LoginWithEmail here as we also add the "forgot password" link.

[djhi]

Nice improvement!

[djhi]

Shouldn't we have a LoginFormWithEmail to make customization even easier (like adding custom content in the simple example)?

[fzaninotto]

I think this would be too many components (not easy to document). Instead, I documented how to pass custom children.