[Feature] Rename Go module and its usages to match new GitHub repository eksctl-io/eksctl

[Himangini]

With eksctl's transition to an open governance model, and now that we have moved to eksctl-io GitHub Org, we need to rename the Go module and all eksctl imports to match the new repository eksctl-io/eksctl.

We plan to move this towards the end of Q4 so the community is well-adjusted to all the recent changes.
If there are any concerns from the community, we'll use the comments under this issue as discussion points.

Related issue: https://github.com/eksctl-io/eksctl-private/issues/828
Related comment: https://github.com/eksctl-io/eksctl-private/pull/1045#pullrequestreview-1464542086

When we plan on refactoring or making any changes to eksctl's public API, we can use it as an opportunity to add a major version suffix /v2 and also rename the module to github.com/eksctl-io/eksctl/v2. That way, users wanting to use the new API will have to change their imports.