Migrate from gopkg.in/square/go-jose.v2 to github.com/go-jose/go-jose/v3

[mtrmac]

https://github.com/square/go-jose/tree/master says the former is deprecated. Moving everything to /v3 will, eventually, allow callers to only contain one vendored implementation instead of up to 3.

[rhatdan]

LGTM