Generate markup for a button widget for a Synapse project wiki.
Refer to widget docs at https://help.synapse.org/docs/Wikis.1975746682.html#Wikis-WikiWidgets.
Buttons should be created sparingly and strategically.
See remove_button
in case of future regret.
Usage
button_widget(label, url, align = c("None", "Left", "Right", "Center"))