provide a className for the button

[michaud]

https://github.com/inrupt/solid-ui-react/blob/266e75b683b788332aa253690f8bbfc93715c5ff/src/components/logIn/index.tsx#L38

https://github.com/inrupt/solid-ui-react/blob/266e75b683b788332aa253690f8bbfc93715c5ff/src/components/logIn/index.tsx#L79

at the moment the button is styled by global styles but most times you would like to be able to customize the button. Passing through the className prop would help with that

const { oidcIssuer, redirectUrl, children, _className,_ authOptions, onError } =

<button _className={ className }_ type="button" onClick={loginHandler} onKeyDown={keyDownHandler}>