Change module name to github.com/oras-project/oras-go/v3

[shizhMSFT]

The oras-go is go module / library with the following go module name defined in go.mod:

oras-go/go.mod

Line 1 in e8225cb

module oras.land/oras-go/v2

Therefore, go get relies on the availability of the website oras.land. Developers and users won't be able to build their applications which invokes oras-go if there is a bad change in oras.land, which is backed by oras-www.

As a solution, it is better to rename the module name under github.com for better stability and availability. Since this is a breaking change, the change should happen for the next generation of oras-go. That is, oras-go v3. The module name will be github.com/oras-project/oras-go/v3.

Slack disucssion: https://cloud-native.slack.com/archives/CJ1KHJM5Z/p1679463144003729