Use correct vmware-tanzu/carvel-imgpkg module name instead of k14s

[jpmcb]

This PR changes references of the k14s/imgpkg go module to be vmware-tanzu/carvel-imgpkg, primarily in the go.mod file. This is required to be able to run

go get github.com/vmware-tanzu/carvel-imgpkg

without errors

Ran ./hack/build-and-lint.sh to verify

Fixes #278

[pivotaljohn]

Thanks for chopping wood, here, @jpmcb.

Gonna mark this as "draft" only to avoid accidentally merging this before we're ready.

Please see comment on #278.

[DennisDenuto]

Thanks for the PR! 🚀 @jpmcb

In order to make this change consistent with other tools in the carvel suite, can you please create a docs/dev.md file with a section documenting the module rename. It is hopefully one way to help inform folk of this rename - if they run into issues.

For more details refer to the "documentation" section: https://github.com/vmware-tanzu/carvel/issues/153

[pivotaljohn]

With those docs in place, we'd be good to just roll forward: pulling out of draft. 👍🏻

[DennisDenuto]

@joaopapereira mentioned at standup he would prefer this PR go in a release without any other changes.

So, that is looking to be v0.22.0.

[jpmcb]

@DennisDenuto - added a docs/dev.md - let me know if there are any other changes y'all want!

[DennisDenuto]

Thanks @jpmcb docs/dev.md look great!!

We plan on having this PR merged/released for v0.22.0