Support fallback download locations

[cristicalin]

What would you like to be added:

Support in the download role for alternate download locations.

Why is this needed:

Project calico decided to shift their release assets download location with 3.21.3 and this breaks our download logic if we want to continue to support older versions that have their assets in the old locations (see https://github.com/projectcalico/calico/releases/tag/v3.21.3 and projectcalico/calico#5421).

To mitigate this issue I propose we modify the download role and implement a fallback logic with alternative download locations so that it would try all mirrors/alternatives if it gets 404s.

/cc @floryut @oomichi @Miouge1

[oomichi]

@cristicalin
Thank you for your proposal.
This fallback download location proposal makes sense to me.