Evaluate adding --assets-links and deprecate --asset-link

Follow-up conversation on --assets-link and --assets-links #66 (comment 688662914)

@steveazz @jaime @ebaque Implementation aside, does it makes sense to have --assets-links to behave as an alias to --assets-link, both accepting single and multiple entries?

To avoid the “decision matrix” @steveazz mentioned, we could eventually deprecate --assets-link.

cc @cbalane @kbychu