Add support for href, target, and rel properties for EuiContextMenu items.

[cjcenizal]

@jen-huang This will give us the option to specify hrefs for the index pattern creation options, instead of using onClick in conjunction with kbnUrl (if we decide that's better).

[jen-huang]

I think this is a useful enhancement, regardless of use for index pattern creation!

LGTM

[jen-huang]

Just to reduce duplication, we could do:

const buttonInner = (
  <span className="euiContextMenu__itemLayout">
    {iconInstance}
    <span className="euiContextMenuItem__text">
      {children}
    </span>
    {arrow}
  </span>
);

And use {buttonInner} inside both <a> and <button>

[cchaos]

I think this is a good rule of thumb because it not only reduces duplication, makes it easier to read, but also makes it easier to update.

[cjcenizal]

Thanks peeps! Good suggestion.