EuiLink should support both href and onClick simultaneously

[chrisdavies]

Currently, EuiLink disallows both href and onClick to be specified. If there is an onClick, EuiLink always renders as an HTML button. But there are scenarios where it is desirable to have an actual a element with an href and onClick, for example, if you wanted to show a confirmation dialog when the user is navigating to an external link.

My proposal is to render a button if href is not provided or is blank, and to otherwise render an a tag.