fix(image-card): render as div if no href is provided

[jendowns]

Closes #514

Currently unless you add the disabled prop, an ImageCard will always render as an anchor.
This is problematic if you don't also provide an href (which is not a required prop, either).

Recently on the IBM Security design team, we've come across a situation where we want the positioning and styling of an ImageCard within a grid, but we don't need to link it anywhere. (So, we aren't providing an href). The ImageGalleryCard would not apply well for our designs/situation., and we also don't want to apply disabled={true} to ImageCard which would apply "do not click" cursor + icon + give an impression that the Card would be clickable under other circumstances. So we wanted to propose a fix here.

Please let me know what you think -- thanks!

Changelog

Changed

• only apply bx--tile--clickable class if href === undefined (for hover effects on links only, etc)
• render ImageCard as a div if href === undefined

[vercel]

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[SimonFinney]

For context, we're currently migrating our experience guide over to use gatsby-theme-carbon under the hood - we'd like to reuse as much as possible and have several instances in which we use ImageCard with no link out to somewhere else.

As a workaround, we thought we could linking directly to the static image but this doesn't play good with Gatsby.

[alisonjoseph]

👍 thanks for adding this!