Annotations in lock file is not preserved during going from tar->registry.

**What steps did you take:**
The goal is I want to install a helm chart to a offline env using kbld and imgpkg to reallocate the images. The procedure I thought in mind was...
```
helm template hoge hoge/foo > manifests/bar.yaml
kbld -f manifests/ --imgpkg-lock-output /tmp/image-lock.yaml
imgpkg copy --lock /tmp/image-lock.yaml --to-tar /tmp/images.tar
--- Go to offline env ----
imgpkg copy --tar /tmp/images.tar --to-repo --lock-output /tmp/image-offline-lock.yaml
helm template hoge hoge/foo | kbld -f- -f /tmp/image-offline-lock.yaml
```
but the last commands errors with the following.

```
ubuntu@ubuntu-449:~$ helm template argo argo/argo-cd | kbld -f- -f /tmp/image-offline-lock.yaml
kbld: Error: Validating imageslock/ (imgpkg.carvel.dev/v1alpha1) cluster:
Validating Overrides[0]:
Expected Image or ImageRepo to be non-empty
```
Annotations are missing in `/tmp/image-offline-lock.yaml`

```
buntu@ubuntu-449:~$ cat /tmp/image-offline-lock.yaml
---
apiVersion: imgpkg.carvel.dev/v1alpha1
images:
- image: harbor.lespaulstudioplus.info/library/imgpkg-demo@sha256:5e88f2205de172b60fd7af23ac92f34321688a83de9f7de7c9a6f394f6950877
- image: harbor.lespaulstudioplus.info/library/imgpkg-demo@sha256:2defd45426be3b5bc7415455ca529c910dab7473717eeece9c3cc26efa5ca037
- image: harbor.lespaulstudioplus.info/library/imgpkg-demo@sha256:6b10107669332f3f68b659f3f13ce33c869d2dcaacdd64fd3e6cf0a7d98b9cd7
- image: harbor.lespaulstudioplus.info/library/imgpkg-demo@sha256:044559541242562493957ab02c3ff7a9a55b8571aa2c8d98e0557b189c2d3968
- image: harbor.lespaulstudioplus.info/library/imgpkg-demo@sha256:e5399090dd46c83d0d5c6f8941f34d87a47ca54fda89221c1dabd2f5beb7ed15
- image: harbor.lespaulstudioplus.info/library/imgpkg-demo@sha256:1f22f3fb44446f752e1457d9b1612d08dc6a808c267fee3ef0488959be83c2a1
- image: harbor.lespaulstudioplus.info/library/imgpkg-demo@sha256:ca760f94b35eb78575b170e41d1e19e27359b29245dacfd1c42ae90452ecc08e
- image: harbor.lespaulstudioplus.info/library/imgpkg-demo@sha256:0f354ec1728d9ff32edcd7d1b8bbdfc798277ad36120dc3dc683be44524c8b60
- image: harbor.lespaulstudioplus.info/library/imgpkg-demo@sha256:0039796b887fd30e460353f14e46ba1004152aa97f5f59094cc21eac445fc89b
- image: harbor.lespaulstudioplus.info/library/imgpkg-demo@sha256:b53a2f76f949849cbe7e0b1e343a2076c7f205cfcfe8116e461e6861369fa81f
kind: ImagesLock
```

**What happened:**
Annotations were lost during tar->registry imgpkg

**What did you expect:**
Annotations should be preserved

**Environment:**

- imgpkg version : 0.17
- Docker registry used (e.g. `Docker HUB`): harbor
- OS (e.g. from `/etc/os-release`): 18.04.5 LTS (Bionic Beaver)

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