Consider shipping release tarball with vendored dependencies

[DanielSun100478]

Discussed in #394

^{Originally posted by illiliti February 13, 2022}
For example, dnscrypt-proxy does this by simply maintaining vendor directory. You can also setup CI to vendor dependencies into release tarball without needing to keep vendor directory within repository. Here is the command that can be used for this: go mod vendor

With vendored dependencies, i can build age from source without internet connection by using this command: go build -mod=vendor