finish support for downloading the code archive

[shiftkey]

This was started in #765 but due to #808 we either need to:

• implement a workaround for users to opt-out of redirects, leave the feature incomplete
• just finish the feature, make retrieving the link unnecessary

I've favoured the latter, and marked the existing GetArchiveLink methods as obsolete.

Doing this as a separate PR into the redirect PR so we can discuss whether users want to access the link without initiating the download.

Fixes #748

cc @alfhenrik

[hnrkndrssn]

Yep, sounds good to me.
Reading the API docs, the purpose of that endpoint is to redirect to the actual content so we should probably adhere to that I guess 😄

And if someone is crying out for functionality to get just the link then we can reconsider and add that back in.

[shiftkey]

Thanks @alfhenrik for the sanity check!

[hnrkndrssn]