theme(fix): remove caching of share links (#757)

You can't just cache the share links, that will result into every blog
post having the same URL.

Just use `partial` on the getShareLink.html. So now each post will show
the correct URL to share the post via social media or alike.

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Signed-off-by: Melroy van den Berg <melroy@melroy.org>
Signed-off-by: Patrick Kollitsch <83281+davidsneighbour@users.noreply.github.com>
Co-authored-by: Patrick Kollitsch <83281+davidsneighbour@users.noreply.github.com>