Pull imgpkg bundle contents from a tarball

**Describe the problem/challenge you have**
I am creating imgpkg bundles for distribution as .tar files.
These bundle contents have CRDs and other resource definitions, and do not have any images that need to be relocated. In order to extract the contents from the bundle, I still have to relocate the tarball to a registry first, which seems odd.
```
imgpkg copy --tar --to-repo
imgpkg pull -b -o /tmp/bundlecontent
kubectl apply -f /tmp/bundlecontent
```
**Describe the solution you'd like**
A CLI that extracts from the tar I downloaded directly to the bundle contents without the need to copy to a registry first.
imgpkg build --tar -o

**Anything else you would like to add:**
This is the reverse/opposite of this issue: https://github.com/vmware-tanzu/carvel-imgpkg/issues/55
Slack thread: https://vmware.slack.com/archives/CUK1X0Z8Q/p1629931739341500
@aaronshurley

---
Vote on this request

This is an invitation to the community to vote on issues, to help us prioritize our backlog. Use the "smiley face" up to the right of this comment to vote.

👍 "I would like to see this addressed as soon as possible"
👎 "There are other more important things to focus on right now"

We are also happy to receive and review Pull Requests if you want to help working on this issue.

Start by tracing the existing `imgpkg copy --tar` and `imgpkg pull -b` command paths and how they read and write bundle tarballs. Add a direct tarball extraction path matching the requested `imgpkg build --tar -o ` interface, then verify that the resulting directory contains the bundle contents without requiring a registry.

Written by the indexing model from the issue text.