Proposal: Custom Go Module Domain for v2

Currently, our Go SDK modules are published under GitHub paths:

`github.com/open-feature/go-sdk/openfeature`
`github.com/open-feature/go-sdk-contrib/...`

and for `v2` we may have something like

`github.com/open-feature/go-sdk/v2/openfeature`
`github.com/open-feature/go-sdk-contrib/v2/...`

I’d like to propose exploring the possibility of using a custom Go module domain for v2, e.g.:

`go.openfeature.dev/openfeature`
`go.openfeature.dev/contrib`

This would make module imports cleaner and more consistent. Tools like [modgen](https://github.com/essaim-dev/modgen) can generate the required static files for a custom domain, though it would require domain and hosting (which may involve a budget).

There are some pros and cons. Introducing a custom domain may add some overhead, especially for new modules or providers in contrib. However, hosting modules under `go.openfeature.dev` may allow us to collect access logs and convert them into meaningful insights, track downloads, and potentially build adoption trends with some additional analytics work.

As we look ahead to `v2`, this could be a great time to implement it if desirable. I’d love to hear your thoughts, and whether you’ve done something similar in the past.